Re: [PATCH 6/7] ovl: intercept mmap

[Amir Goldstein]

On Thu, Nov 24, 2016 at 8:03 PM, Amir Goldstein  wrote:
> On Thu, Nov 24, 2016 at 3:25 PM, Amir Goldstein  wrote:
>> On Thu, Nov 24, 2016 at 12:55 PM, Miklos Szeredi  wrote:
>>> ... in order to handle the corner case when the file is copied up after
>>> being opened read-only and mapped shared.
>>>
>>> Can be verified with the following script:
>>>
>>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>>> cd /
>>> rm -rf /tmp/ovl-rorw-test
>>> mkdir /tmp/ovl-rorw-test
>>> cd /tmp/ovl-rorw-test
>>> cat << EOF > rorw-map.c
>>> #include 
>>> #include 
>>> #include 
>>> #include 
>>> #include 
>>>
>>> int main(int argc, char *argv[])
>>> {
>>> int rofd, rwfd;
>>> int ret;
>>> char buf[4];
>>> char *addr;
>>>
>>> rofd = open(argv[1], O_RDONLY);
>>> if (rofd == -1)
>>> err(1, "ro open");
>>>
>>> addr = mmap(NULL, 4, PROT_READ, MAP_SHARED, rofd, 0);
>>> if (addr == MAP_FAILED)
>>> err(1, "ro mmap");
>>>
>>> if (memcmp(addr, "bubu", 4) == 0)
>>> errx(1, "identical startup data");
>>>
>>> rwfd = open(argv[1], O_WRONLY);
>>> if (rwfd == -1)
>>> err(1, "rw open");
>>>
>>> ret = write(rwfd, "bubu", 4);
>>> if (ret == -1)
>>> err(1, "write");
>>> if (ret < 4)
>>> errx(1, "short write");
>>>
>>> if (memcmp(addr, "bubu", 4) != 0)
>>> errx(1, "bad mmap data");
>>>
>>> ret = read(rofd, buf, 4);
>>> if (ret == -1)
>>> err(1, "read");
>>> if (ret < 4)
>>> errx(1, "short read");
>>> if (memcmp(buf, "bubu", 4) != 0)
>>> errx(1, "bad read data");
>>>
>>> return 0;
>>> }
>>> EOF
>>
>>
>> Good timing :-)
>> I just started working on an xfstest this morning to bring this corner
>> case into attention.
>> Once I get the xfs_io commands in order, you could use them for a
>> shorter commit message.
>> Unless you like it that way...
>>
>>> gcc -o rorw-map rorw-map.c
>>> mkdir -p mnt lower upper work
>>> echo baba > lower/foo
>>> mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work mnt
>>> ./rorw-map mnt/foo
>
> Well, there is a bug/feature is xfs_io that puts it in a spin when an
> open command is
> used from command line, so I will need to fix that before sumbitting
> the xfstest, but for
> documentation purpose, you can use the following command in place of rorw-map:
>
> $ xfs_io -r -c "mmap -r 0 4" -c "open foo" -c "pwrite -S 0x61 0 4" -c
> "mread -v 0 4" foo |tail -n 1
> :  62 61 62 61  baba
>
> Naturally, 'baba' is bad. '' is good.
>

Or maybe it was meant to be used this way, which does not blow up:

$ xfs_io << EOF
open -r foo
mmap -r 0 4
open foo
pwrite -S 0x61 0 4
mread -v 0 4
EOF

>>> umount mnt
>>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>>>
>>> No output means success, "rorw-map: bad mmap data" means failure.
>>>
>>> Signed-off-by: Miklos Szeredi 
>>> ---
>>>  fs/overlayfs/inode.c | 23 ++-
>>>  1 file changed, 22 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>>> index 09c6f99bd5db..25b31c6ebe9e 100644
>>> --- a/fs/overlayfs/inode.c
>>> +++ b/fs/overlayfs/inode.c
>>> @@ -11,6 +11,7 @@
>>>  #include 
>>>  #include 
>>>  #include 
>>> +#include 
>>>  #include 
>>>  #include 
>>>  #include 
>>> @@ -392,6 +393,25 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, 
>>> struct iov_iter *to)
>>> return ret;
>>>  }
>>>
>>> +static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
>>> +{
>>> +   if (likely(ovl_file_is_lower(file)))
>>> +   return OVL_CALL_REAL_FOP(file, mmap(file, vma));
>>> +
>>> +   file = filp_clone_open(file);
>>> +   if (IS_ERR(file))
>>> +   return PTR_ERR(file);
>>> +
>>> +   fput(vma->vm_file);
>>> +   /* transfer ref: */
>>> +   vma->vm_file = file;
>>> +
>>> +   if (!file->f_op->mmap)
>>> +   return -ENODEV;
>>> +
>>> +   return file->f_op->mmap(file, vma);
>>> +}
>>> +
>>>  static struct ovl_fops *ovl_fops_find(const struct file_operations *orig)
>>>  {
>>> struct ovl_fops *ofop;
>>> @@ -431,9 +451,10 @@ static struct ovl_fops *ovl_fops_get(struct file *file)
>>> /* Intercept these: */
>>> if (orig->read_iter)
>>> ofop->fops.read_iter = ovl_read_iter;
>>> +   if (orig->mmap)
>>> +   ofop->fops.mmap = ovl_mmap;
>>>
>>> /* These will need to be intercepted: */
>>> -   ofop->fops.mmap = orig->mmap;
>>> ofop->fops.fsync = orig->fsync;
>>>
>>> /*
>>> --
>>> 2.5.5
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
>>> the body 

Re: [PATCH 6/7] ovl: intercept mmap

[Amir Goldstein]

On Thu, Nov 24, 2016 at 8:03 PM, Amir Goldstein  wrote:
> On Thu, Nov 24, 2016 at 3:25 PM, Amir Goldstein  wrote:
>> On Thu, Nov 24, 2016 at 12:55 PM, Miklos Szeredi  wrote:
>>> ... in order to handle the corner case when the file is copied up after
>>> being opened read-only and mapped shared.
>>>
>>> Can be verified with the following script:
>>>
>>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>>> cd /
>>> rm -rf /tmp/ovl-rorw-test
>>> mkdir /tmp/ovl-rorw-test
>>> cd /tmp/ovl-rorw-test
>>> cat << EOF > rorw-map.c
>>> #include 
>>> #include 
>>> #include 
>>> #include 
>>> #include 
>>>
>>> int main(int argc, char *argv[])
>>> {
>>> int rofd, rwfd;
>>> int ret;
>>> char buf[4];
>>> char *addr;
>>>
>>> rofd = open(argv[1], O_RDONLY);
>>> if (rofd == -1)
>>> err(1, "ro open");
>>>
>>> addr = mmap(NULL, 4, PROT_READ, MAP_SHARED, rofd, 0);
>>> if (addr == MAP_FAILED)
>>> err(1, "ro mmap");
>>>
>>> if (memcmp(addr, "bubu", 4) == 0)
>>> errx(1, "identical startup data");
>>>
>>> rwfd = open(argv[1], O_WRONLY);
>>> if (rwfd == -1)
>>> err(1, "rw open");
>>>
>>> ret = write(rwfd, "bubu", 4);
>>> if (ret == -1)
>>> err(1, "write");
>>> if (ret < 4)
>>> errx(1, "short write");
>>>
>>> if (memcmp(addr, "bubu", 4) != 0)
>>> errx(1, "bad mmap data");
>>>
>>> ret = read(rofd, buf, 4);
>>> if (ret == -1)
>>> err(1, "read");
>>> if (ret < 4)
>>> errx(1, "short read");
>>> if (memcmp(buf, "bubu", 4) != 0)
>>> errx(1, "bad read data");
>>>
>>> return 0;
>>> }
>>> EOF
>>
>>
>> Good timing :-)
>> I just started working on an xfstest this morning to bring this corner
>> case into attention.
>> Once I get the xfs_io commands in order, you could use them for a
>> shorter commit message.
>> Unless you like it that way...
>>
>>> gcc -o rorw-map rorw-map.c
>>> mkdir -p mnt lower upper work
>>> echo baba > lower/foo
>>> mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work mnt
>>> ./rorw-map mnt/foo
>
> Well, there is a bug/feature is xfs_io that puts it in a spin when an
> open command is
> used from command line, so I will need to fix that before sumbitting
> the xfstest, but for
> documentation purpose, you can use the following command in place of rorw-map:
>
> $ xfs_io -r -c "mmap -r 0 4" -c "open foo" -c "pwrite -S 0x61 0 4" -c
> "mread -v 0 4" foo |tail -n 1
> :  62 61 62 61  baba
>
> Naturally, 'baba' is bad. '' is good.
>

Or maybe it was meant to be used this way, which does not blow up:

$ xfs_io << EOF
open -r foo
mmap -r 0 4
open foo
pwrite -S 0x61 0 4
mread -v 0 4
EOF

>>> umount mnt
>>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>>>
>>> No output means success, "rorw-map: bad mmap data" means failure.
>>>
>>> Signed-off-by: Miklos Szeredi 
>>> ---
>>>  fs/overlayfs/inode.c | 23 ++-
>>>  1 file changed, 22 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>>> index 09c6f99bd5db..25b31c6ebe9e 100644
>>> --- a/fs/overlayfs/inode.c
>>> +++ b/fs/overlayfs/inode.c
>>> @@ -11,6 +11,7 @@
>>>  #include 
>>>  #include 
>>>  #include 
>>> +#include 
>>>  #include 
>>>  #include 
>>>  #include 
>>> @@ -392,6 +393,25 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, 
>>> struct iov_iter *to)
>>> return ret;
>>>  }
>>>
>>> +static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
>>> +{
>>> +   if (likely(ovl_file_is_lower(file)))
>>> +   return OVL_CALL_REAL_FOP(file, mmap(file, vma));
>>> +
>>> +   file = filp_clone_open(file);
>>> +   if (IS_ERR(file))
>>> +   return PTR_ERR(file);
>>> +
>>> +   fput(vma->vm_file);
>>> +   /* transfer ref: */
>>> +   vma->vm_file = file;
>>> +
>>> +   if (!file->f_op->mmap)
>>> +   return -ENODEV;
>>> +
>>> +   return file->f_op->mmap(file, vma);
>>> +}
>>> +
>>>  static struct ovl_fops *ovl_fops_find(const struct file_operations *orig)
>>>  {
>>> struct ovl_fops *ofop;
>>> @@ -431,9 +451,10 @@ static struct ovl_fops *ovl_fops_get(struct file *file)
>>> /* Intercept these: */
>>> if (orig->read_iter)
>>> ofop->fops.read_iter = ovl_read_iter;
>>> +   if (orig->mmap)
>>> +   ofop->fops.mmap = ovl_mmap;
>>>
>>> /* These will need to be intercepted: */
>>> -   ofop->fops.mmap = orig->mmap;
>>> ofop->fops.fsync = orig->fsync;
>>>
>>> /*
>>> --
>>> 2.5.5
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
>>> the body of a message to majord...@vger.kernel.org
>>> More majordomo info at  

Re: [PATCH 6/7] ovl: intercept mmap

[Amir Goldstein]

On Thu, Nov 24, 2016 at 3:25 PM, Amir Goldstein  wrote:
> On Thu, Nov 24, 2016 at 12:55 PM, Miklos Szeredi  wrote:
>> ... in order to handle the corner case when the file is copied up after
>> being opened read-only and mapped shared.
>>
>> Can be verified with the following script:
>>
>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>> cd /
>> rm -rf /tmp/ovl-rorw-test
>> mkdir /tmp/ovl-rorw-test
>> cd /tmp/ovl-rorw-test
>> cat << EOF > rorw-map.c
>> #include 
>> #include 
>> #include 
>> #include 
>> #include 
>>
>> int main(int argc, char *argv[])
>> {
>> int rofd, rwfd;
>> int ret;
>> char buf[4];
>> char *addr;
>>
>> rofd = open(argv[1], O_RDONLY);
>> if (rofd == -1)
>> err(1, "ro open");
>>
>> addr = mmap(NULL, 4, PROT_READ, MAP_SHARED, rofd, 0);
>> if (addr == MAP_FAILED)
>> err(1, "ro mmap");
>>
>> if (memcmp(addr, "bubu", 4) == 0)
>> errx(1, "identical startup data");
>>
>> rwfd = open(argv[1], O_WRONLY);
>> if (rwfd == -1)
>> err(1, "rw open");
>>
>> ret = write(rwfd, "bubu", 4);
>> if (ret == -1)
>> err(1, "write");
>> if (ret < 4)
>> errx(1, "short write");
>>
>> if (memcmp(addr, "bubu", 4) != 0)
>> errx(1, "bad mmap data");
>>
>> ret = read(rofd, buf, 4);
>> if (ret == -1)
>> err(1, "read");
>> if (ret < 4)
>> errx(1, "short read");
>> if (memcmp(buf, "bubu", 4) != 0)
>> errx(1, "bad read data");
>>
>> return 0;
>> }
>> EOF
>
>
> Good timing :-)
> I just started working on an xfstest this morning to bring this corner
> case into attention.
> Once I get the xfs_io commands in order, you could use them for a
> shorter commit message.
> Unless you like it that way...
>
>> gcc -o rorw-map rorw-map.c
>> mkdir -p mnt lower upper work
>> echo baba > lower/foo
>> mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work mnt
>> ./rorw-map mnt/foo

Well, there is a bug/feature is xfs_io that puts it in a spin when an
open command is
used from command line, so I will need to fix that before sumbitting
the xfstest, but for
documentation purpose, you can use the following command in place of rorw-map:

$ xfs_io -r -c "mmap -r 0 4" -c "open foo" -c "pwrite -S 0x61 0 4" -c
"mread -v 0 4" foo |tail -n 1
:  62 61 62 61  baba

Naturally, 'baba' is bad. '' is good.

>> umount mnt
>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>>
>> No output means success, "rorw-map: bad mmap data" means failure.
>>
>> Signed-off-by: Miklos Szeredi 
>> ---
>>  fs/overlayfs/inode.c | 23 ++-
>>  1 file changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>> index 09c6f99bd5db..25b31c6ebe9e 100644
>> --- a/fs/overlayfs/inode.c
>> +++ b/fs/overlayfs/inode.c
>> @@ -11,6 +11,7 @@
>>  #include 
>>  #include 
>>  #include 
>> +#include 
>>  #include 
>>  #include 
>>  #include 
>> @@ -392,6 +393,25 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct 
>> iov_iter *to)
>> return ret;
>>  }
>>
>> +static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
>> +{
>> +   if (likely(ovl_file_is_lower(file)))
>> +   return OVL_CALL_REAL_FOP(file, mmap(file, vma));
>> +
>> +   file = filp_clone_open(file);
>> +   if (IS_ERR(file))
>> +   return PTR_ERR(file);
>> +
>> +   fput(vma->vm_file);
>> +   /* transfer ref: */
>> +   vma->vm_file = file;
>> +
>> +   if (!file->f_op->mmap)
>> +   return -ENODEV;
>> +
>> +   return file->f_op->mmap(file, vma);
>> +}
>> +
>>  static struct ovl_fops *ovl_fops_find(const struct file_operations *orig)
>>  {
>> struct ovl_fops *ofop;
>> @@ -431,9 +451,10 @@ static struct ovl_fops *ovl_fops_get(struct file *file)
>> /* Intercept these: */
>> if (orig->read_iter)
>> ofop->fops.read_iter = ovl_read_iter;
>> +   if (orig->mmap)
>> +   ofop->fops.mmap = ovl_mmap;
>>
>> /* These will need to be intercepted: */
>> -   ofop->fops.mmap = orig->mmap;
>> ofop->fops.fsync = orig->fsync;
>>
>> /*
>> --
>> 2.5.5
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
>> the body of a message to majord...@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 6/7] ovl: intercept mmap

[Amir Goldstein]

On Thu, Nov 24, 2016 at 3:25 PM, Amir Goldstein  wrote:
> On Thu, Nov 24, 2016 at 12:55 PM, Miklos Szeredi  wrote:
>> ... in order to handle the corner case when the file is copied up after
>> being opened read-only and mapped shared.
>>
>> Can be verified with the following script:
>>
>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>> cd /
>> rm -rf /tmp/ovl-rorw-test
>> mkdir /tmp/ovl-rorw-test
>> cd /tmp/ovl-rorw-test
>> cat << EOF > rorw-map.c
>> #include 
>> #include 
>> #include 
>> #include 
>> #include 
>>
>> int main(int argc, char *argv[])
>> {
>> int rofd, rwfd;
>> int ret;
>> char buf[4];
>> char *addr;
>>
>> rofd = open(argv[1], O_RDONLY);
>> if (rofd == -1)
>> err(1, "ro open");
>>
>> addr = mmap(NULL, 4, PROT_READ, MAP_SHARED, rofd, 0);
>> if (addr == MAP_FAILED)
>> err(1, "ro mmap");
>>
>> if (memcmp(addr, "bubu", 4) == 0)
>> errx(1, "identical startup data");
>>
>> rwfd = open(argv[1], O_WRONLY);
>> if (rwfd == -1)
>> err(1, "rw open");
>>
>> ret = write(rwfd, "bubu", 4);
>> if (ret == -1)
>> err(1, "write");
>> if (ret < 4)
>> errx(1, "short write");
>>
>> if (memcmp(addr, "bubu", 4) != 0)
>> errx(1, "bad mmap data");
>>
>> ret = read(rofd, buf, 4);
>> if (ret == -1)
>> err(1, "read");
>> if (ret < 4)
>> errx(1, "short read");
>> if (memcmp(buf, "bubu", 4) != 0)
>> errx(1, "bad read data");
>>
>> return 0;
>> }
>> EOF
>
>
> Good timing :-)
> I just started working on an xfstest this morning to bring this corner
> case into attention.
> Once I get the xfs_io commands in order, you could use them for a
> shorter commit message.
> Unless you like it that way...
>
>> gcc -o rorw-map rorw-map.c
>> mkdir -p mnt lower upper work
>> echo baba > lower/foo
>> mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work mnt
>> ./rorw-map mnt/foo

Well, there is a bug/feature is xfs_io that puts it in a spin when an
open command is
used from command line, so I will need to fix that before sumbitting
the xfstest, but for
documentation purpose, you can use the following command in place of rorw-map:

$ xfs_io -r -c "mmap -r 0 4" -c "open foo" -c "pwrite -S 0x61 0 4" -c
"mread -v 0 4" foo |tail -n 1
:  62 61 62 61  baba

Naturally, 'baba' is bad. '' is good.

>> umount mnt
>>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>>
>> No output means success, "rorw-map: bad mmap data" means failure.
>>
>> Signed-off-by: Miklos Szeredi 
>> ---
>>  fs/overlayfs/inode.c | 23 ++-
>>  1 file changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>> index 09c6f99bd5db..25b31c6ebe9e 100644
>> --- a/fs/overlayfs/inode.c
>> +++ b/fs/overlayfs/inode.c
>> @@ -11,6 +11,7 @@
>>  #include 
>>  #include 
>>  #include 
>> +#include 
>>  #include 
>>  #include 
>>  #include 
>> @@ -392,6 +393,25 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct 
>> iov_iter *to)
>> return ret;
>>  }
>>
>> +static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
>> +{
>> +   if (likely(ovl_file_is_lower(file)))
>> +   return OVL_CALL_REAL_FOP(file, mmap(file, vma));
>> +
>> +   file = filp_clone_open(file);
>> +   if (IS_ERR(file))
>> +   return PTR_ERR(file);
>> +
>> +   fput(vma->vm_file);
>> +   /* transfer ref: */
>> +   vma->vm_file = file;
>> +
>> +   if (!file->f_op->mmap)
>> +   return -ENODEV;
>> +
>> +   return file->f_op->mmap(file, vma);
>> +}
>> +
>>  static struct ovl_fops *ovl_fops_find(const struct file_operations *orig)
>>  {
>> struct ovl_fops *ofop;
>> @@ -431,9 +451,10 @@ static struct ovl_fops *ovl_fops_get(struct file *file)
>> /* Intercept these: */
>> if (orig->read_iter)
>> ofop->fops.read_iter = ovl_read_iter;
>> +   if (orig->mmap)
>> +   ofop->fops.mmap = ovl_mmap;
>>
>> /* These will need to be intercepted: */
>> -   ofop->fops.mmap = orig->mmap;
>> ofop->fops.fsync = orig->fsync;
>>
>> /*
>> --
>> 2.5.5
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
>> the body of a message to majord...@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 6/7] ovl: intercept mmap

[Amir Goldstein]

On Thu, Nov 24, 2016 at 12:55 PM, Miklos Szeredi  wrote:
> ... in order to handle the corner case when the file is copied up after
> being opened read-only and mapped shared.
>
> Can be verified with the following script:
>
>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
> cd /
> rm -rf /tmp/ovl-rorw-test
> mkdir /tmp/ovl-rorw-test
> cd /tmp/ovl-rorw-test
> cat << EOF > rorw-map.c
> #include 
> #include 
> #include 
> #include 
> #include 
>
> int main(int argc, char *argv[])
> {
> int rofd, rwfd;
> int ret;
> char buf[4];
> char *addr;
>
> rofd = open(argv[1], O_RDONLY);
> if (rofd == -1)
> err(1, "ro open");
>
> addr = mmap(NULL, 4, PROT_READ, MAP_SHARED, rofd, 0);
> if (addr == MAP_FAILED)
> err(1, "ro mmap");
>
> if (memcmp(addr, "bubu", 4) == 0)
> errx(1, "identical startup data");
>
> rwfd = open(argv[1], O_WRONLY);
> if (rwfd == -1)
> err(1, "rw open");
>
> ret = write(rwfd, "bubu", 4);
> if (ret == -1)
> err(1, "write");
> if (ret < 4)
> errx(1, "short write");
>
> if (memcmp(addr, "bubu", 4) != 0)
> errx(1, "bad mmap data");
>
> ret = read(rofd, buf, 4);
> if (ret == -1)
> err(1, "read");
> if (ret < 4)
> errx(1, "short read");
> if (memcmp(buf, "bubu", 4) != 0)
> errx(1, "bad read data");
>
> return 0;
> }
> EOF


Good timing :-)
I just started working on an xfstest this morning to bring this corner
case into attention.
Once I get the xfs_io commands in order, you could use them for a
shorter commit message.
Unless you like it that way...

> gcc -o rorw-map rorw-map.c
> mkdir -p mnt lower upper work
> echo baba > lower/foo
> mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work mnt
> ./rorw-map mnt/foo
> umount mnt
>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>
> No output means success, "rorw-map: bad mmap data" means failure.
>
> Signed-off-by: Miklos Szeredi 
> ---
>  fs/overlayfs/inode.c | 23 ++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 09c6f99bd5db..25b31c6ebe9e 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -11,6 +11,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
>  #include 
> @@ -392,6 +393,25 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct 
> iov_iter *to)
> return ret;
>  }
>
> +static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> +   if (likely(ovl_file_is_lower(file)))
> +   return OVL_CALL_REAL_FOP(file, mmap(file, vma));
> +
> +   file = filp_clone_open(file);
> +   if (IS_ERR(file))
> +   return PTR_ERR(file);
> +
> +   fput(vma->vm_file);
> +   /* transfer ref: */
> +   vma->vm_file = file;
> +
> +   if (!file->f_op->mmap)
> +   return -ENODEV;
> +
> +   return file->f_op->mmap(file, vma);
> +}
> +
>  static struct ovl_fops *ovl_fops_find(const struct file_operations *orig)
>  {
> struct ovl_fops *ofop;
> @@ -431,9 +451,10 @@ static struct ovl_fops *ovl_fops_get(struct file *file)
> /* Intercept these: */
> if (orig->read_iter)
> ofop->fops.read_iter = ovl_read_iter;
> +   if (orig->mmap)
> +   ofop->fops.mmap = ovl_mmap;
>
> /* These will need to be intercepted: */
> -   ofop->fops.mmap = orig->mmap;
> ofop->fops.fsync = orig->fsync;
>
> /*
> --
> 2.5.5
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 6/7] ovl: intercept mmap

[Amir Goldstein]

On Thu, Nov 24, 2016 at 12:55 PM, Miklos Szeredi  wrote:
> ... in order to handle the corner case when the file is copied up after
> being opened read-only and mapped shared.
>
> Can be verified with the following script:
>
>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
> cd /
> rm -rf /tmp/ovl-rorw-test
> mkdir /tmp/ovl-rorw-test
> cd /tmp/ovl-rorw-test
> cat << EOF > rorw-map.c
> #include 
> #include 
> #include 
> #include 
> #include 
>
> int main(int argc, char *argv[])
> {
> int rofd, rwfd;
> int ret;
> char buf[4];
> char *addr;
>
> rofd = open(argv[1], O_RDONLY);
> if (rofd == -1)
> err(1, "ro open");
>
> addr = mmap(NULL, 4, PROT_READ, MAP_SHARED, rofd, 0);
> if (addr == MAP_FAILED)
> err(1, "ro mmap");
>
> if (memcmp(addr, "bubu", 4) == 0)
> errx(1, "identical startup data");
>
> rwfd = open(argv[1], O_WRONLY);
> if (rwfd == -1)
> err(1, "rw open");
>
> ret = write(rwfd, "bubu", 4);
> if (ret == -1)
> err(1, "write");
> if (ret < 4)
> errx(1, "short write");
>
> if (memcmp(addr, "bubu", 4) != 0)
> errx(1, "bad mmap data");
>
> ret = read(rofd, buf, 4);
> if (ret == -1)
> err(1, "read");
> if (ret < 4)
> errx(1, "short read");
> if (memcmp(buf, "bubu", 4) != 0)
> errx(1, "bad read data");
>
> return 0;
> }
> EOF


Good timing :-)
I just started working on an xfstest this morning to bring this corner
case into attention.
Once I get the xfs_io commands in order, you could use them for a
shorter commit message.
Unless you like it that way...

> gcc -o rorw-map rorw-map.c
> mkdir -p mnt lower upper work
> echo baba > lower/foo
> mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work mnt
> ./rorw-map mnt/foo
> umount mnt
>  - 8< - - - - - 8< - - - - - 8< - - - - - 8< - - - -
>
> No output means success, "rorw-map: bad mmap data" means failure.
>
> Signed-off-by: Miklos Szeredi 
> ---
>  fs/overlayfs/inode.c | 23 ++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 09c6f99bd5db..25b31c6ebe9e 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -11,6 +11,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>  #include 
>  #include 
>  #include 
> @@ -392,6 +393,25 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct 
> iov_iter *to)
> return ret;
>  }
>
> +static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> +   if (likely(ovl_file_is_lower(file)))
> +   return OVL_CALL_REAL_FOP(file, mmap(file, vma));
> +
> +   file = filp_clone_open(file);
> +   if (IS_ERR(file))
> +   return PTR_ERR(file);
> +
> +   fput(vma->vm_file);
> +   /* transfer ref: */
> +   vma->vm_file = file;
> +
> +   if (!file->f_op->mmap)
> +   return -ENODEV;
> +
> +   return file->f_op->mmap(file, vma);
> +}
> +
>  static struct ovl_fops *ovl_fops_find(const struct file_operations *orig)
>  {
> struct ovl_fops *ofop;
> @@ -431,9 +451,10 @@ static struct ovl_fops *ovl_fops_get(struct file *file)
> /* Intercept these: */
> if (orig->read_iter)
> ofop->fops.read_iter = ovl_read_iter;
> +   if (orig->mmap)
> +   ofop->fops.mmap = ovl_mmap;
>
> /* These will need to be intercepted: */
> -   ofop->fops.mmap = orig->mmap;
> ofop->fops.fsync = orig->fsync;
>
> /*
> --
> 2.5.5
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html