The loff_t type may be wider than phys_addr_t (e.g. on 32-bit systems).
Consequently, the file offset may be truncated in the assignment.
Currently, /dev/mem wraps around, which may cause applications to read
or write incorrect regions of memory by accident.
Let's follow POSIX file semantics here and return 0 when reading from
and -EFBIG when writing to an offset that cannot be represented by a
phys_addr_t.
Note that the conditional is optimized out by the compiler if loff_t
has the same size as phys_addr_t.
Signed-off-by: Petr Tesarik <ptesa...@suse.cz>
---
drivers/char/mem.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 92c5937..917403f 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -99,6 +99,9 @@ static ssize_t read_mem(struct file *file, char
__user *buf, ssize_t read, sz;
char *ptr;
+ if (p != *ppos)
+ return 0;
+
if (!valid_phys_addr_range(p, count))
return -EFAULT;
read = 0;
@@ -157,6 +160,9 @@ static ssize_t write_mem(struct file *file, const
char __user *buf, unsigned long copied;
void *ptr;
+ if (p != *ppos)
+ return -EFBIG;
+
if (!valid_phys_addr_range(p, count))
return -EFAULT;
--
1.8.4.5
--
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