Newly created file on btrfs inherits inode flags from parent directory,
so new inode created in append-only directory has S_APPEND flag set,
may_open() called by do_last() checks that flag then returns -EPERM,
but at that time the new inode is already created.
This can be reproduced by:
# mkdir -p /mnt/btrfs/append-only
# chattr +a /mnt/btrfs/append-only
# ./opentest /mnt/btrfs/append-only/newtestfile
# ls -l /mnt/btrfs/append-only/newtestfile
opentest will return 'Operation not permitted', but the ls shows that
newtestfile is already created.
# cat opentest.c
#include <stdio.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
int main(int argc, char *argv[])
{
int fd;
fd = open(argv[1], O_RDWR|O_CREAT, 0666);
if (fd == -1)
perror("open failed");
return 0;
}
To avoid this, check BTRFS_INODE_APPEND flag first in btrfs_create before
really allocating new inode.
Cc: Chris Mason <chris.ma...@oracle.com>
Signed-off-by: Eryu Guan <guane...@gmail.com>
---
fs/btrfs/inode.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b2d004a..18e9914 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -38,6 +38,7 @@
#include <linux/falloc.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
+#include <linux/namei.h>
#include "compat.h"
#include "ctree.h"
#include "disk-io.h"
@@ -4718,10 +4719,19 @@ static int btrfs_create(struct inode *dir, struct
dentry *dentry,
struct inode *inode = NULL;
int drop_inode = 0;
int err;
+ int open_flag = nd->intent.open.file->f_flags;
unsigned long nr = 0;
u64 objectid;
u64 index = 0;
+ if (BTRFS_I(dir)->flags & BTRFS_INODE_APPEND) {
+ if ((open_flag & O_ACCMODE) != O_RDONLY &&
+ !(open_flag & O_APPEND))
+ return -EPERM;
+ if (open_flag & O_TRUNC)
+ return -EPERM;
+ }
+
/*
* 2 for inode item and ref
* 2 for dir items
--
1.7.7.1
--
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