staging/android: sync_debug: unproxify debugfs files' fops

PATCH In review Nicolai Stange 2 participants 2 messages May 27, 2016 Staging

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Nicolai Stange

author

2016-05-27 18:04 UTC #0 lore raw

PATCH 1/1 staging/android: sync_debug: unproxify debugfs files' fops

Since commit 49d200deaa68 ("debugfs: prevent access to removed files' private data"), a debugfs file's file_operations methods get proxied through lifetime aware wrappers.

However, only a certain subset of the file_operations members is supported by debugfs and ->compat_ioctl isn't among them -- it appears to be NULL from the VFS layer's perspective.

This behaviour breaks the /sys/kernel/debug/sync/sw_sync file introduced concurrently with commit a44eb74cd413 ("staging/android: move SW_SYNC_USER to a debugfs file").

Since that file never gets removed, there is no file removal race and thus, a lifetime checking proxy isn't needed.

Avoid the proxying for /sys/kernel/debug/sync/sw_sync by creating it via debugfs_create_file_unsafe() rather than debugfs_create_file(). For consistency, do the same for /sys/kernel/debug/sync/info.

Fixes 49d200deaa68 ("debugfs: prevent access to removed files' private

                      data")

Fixes a44eb74cd413 ("staging/android: move SW_SYNC_USER to a debugfs

                      file")

Signed-off-by Nicolai Stange <[email protected]>

---
Applicable to linux-next-20160527.
x86_64 allmodconfig build succeeds w/o any new warnings.

Related discussion can be found here:
http://lkml.kernel.org/g/[email protected]

 drivers/staging/android/sync_debug.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

drivers/staging/android/sync_debug.c +9 -3

index 5f57499..1197f9e 100644
@@ -326,9 +326,15 @@ static __init int sync_debugfs_init(void)
 {
 	dbgfs = debugfs_create_dir("sync", NULL);
 
-	debugfs_create_file("info", 0444, dbgfs, NULL, &sync_info_debugfs_fops);
-	debugfs_create_file("sw_sync", 0644, dbgfs, NULL,
-			    &sw_sync_debugfs_fops);
+	/*
+	 * The debugfs files won't ever get removed and thus, there is
+	 * no need to protect it against removal races. The use of
+	 * debugfs_create_file_unsafe() is actually safe here.
+	 */
+	debugfs_create_file_unsafe("info", 0444, dbgfs, NULL,
+				   &sync_info_debugfs_fops);
+	debugfs_create_file_unsafe("sw_sync", 0644, dbgfs, NULL,
+				   &sw_sync_debugfs_fops);
 
 	return 0;
 }

Signature · 1 line

2.8.2

Greg Kroah-Hartman

maintainer

2016-05-27 18:15 UTC #1 lore raw

Quoted 28 lines · Nicolai Stange

Since commit 49d200deaa68 ("debugfs: prevent access to removed files' private data"), a debugfs file's file_operations methods get proxied through lifetime aware wrappers.
However, only a certain subset of the file_operations members is supported by debugfs and ->compat_ioctl isn't among them -- it appears to be NULL from the VFS layer's perspective.
This behaviour breaks the /sys/kernel/debug/sync/sw_sync file introduced concurrently with commit a44eb74cd413 ("staging/android: move SW_SYNC_USER to a debugfs file").
Since that file never gets removed, there is no file removal race and thus, a lifetime checking proxy isn't needed.
Avoid the proxying for /sys/kernel/debug/sync/sw_sync by creating it via debugfs_create_file_unsafe() rather than debugfs_create_file(). For consistency, do the same for /sys/kernel/debug/sync/info.
Fixes 49d200deaa68 ("debugfs: prevent access to removed files' private
                      data")
Fixes a44eb74cd413 ("staging/android: move SW_SYNC_USER to a debugfs
                      file")
Signed-off-by Nicolai Stange <[email protected]>
---
Applicable to linux-next-20160527.
x86_64 allmodconfig build succeeds w/o any new warnings.

Quoted 5 lines

Related discussion can be found here:
http://lkml.kernel.org/g/[email protected]
 drivers/staging/android/sync_debug.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

Thanks, will queue this up after 4.7-rc1 is out.

greg k-h