[PATCH] vfs: get inode after passing previous check in rw_verify_area()

[PATCH] vfs: get inode after passing previous check in rw_verify_area()

[lorneli.cs]

From: Lorne Li <lorneli.cs@gmail.com>

Move file_inode function to the front of line actually using inode.

Signed-off-by: Lorne Li <lorneli.cs@gmail.com>
---
 fs/read_write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 153f8f6..ab63e87 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -368,7 +368,6 @@ int rw_verify_area(int read_write, struct file *file, const loff_t *ppos, size_t
 	loff_t pos;
 	int retval = -EINVAL;
 
-	inode = file_inode(file);
 	if (unlikely((ssize_t) count < 0))
 		return retval;
 	pos = *ppos;
@@ -382,6 +381,7 @@ int rw_verify_area(int read_write, struct file *file, const loff_t *ppos, size_t
 			return retval;
 	}
 
+	inode = file_inode(file);
 	if (unlikely(inode->i_flctx && mandatory_lock(inode))) {
 		retval = locks_mandatory_area(inode, file, pos, pos + count - 1,
 				read_write == READ ? F_RDLCK : F_WRLCK);
-- 
1.8.3.1

Re: [PATCH] vfs: get inode after passing previous check in rw_verify_area()

[Christoph Hellwig]

On Thu, Jun 21, 2018 at 06:29:33PM +0800, lorneli.cs@gmail.com wrote:
> From: Lorne Li <lorneli.cs@gmail.com>
> 
> Move file_inode function to the front of line actually using inode.

Why?

Re: [PATCH] vfs: get inode after passing previous check in rw_verify_area()

[Lorne Li]

If previous check (pos and overflow check) fails, there's no chance to

use variable inode, initialized by file_inode func in the beginning.

So delay the operation until actuallyneeding inode for check.


Maybe I should add a more detailed commit message.


On 2018/6/21 20:22, Christoph Hellwig wrote:
> On Thu, Jun 21, 2018 at 06:29:33PM +0800, lorneli.cs@gmail.com wrote:
>> From: Lorne Li <lorneli.cs@gmail.com>
>>
>> Move file_inode function to the front of line actually using inode.
> Why?