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authorJ. Bruce Fields <bfields@citi.umich.edu>2008-04-14 15:03:02 -0400
committerChris Wright <chrisw@sous-sol.org>2008-04-18 18:53:30 -0700
commitfa4bf970097e80c3ba50467a8b99c8f97a6391f0 (patch)
tree6616f1f9dc110967ce555b4fac0b872443e08a71
parent44996dccd89ce86c7c38e37e0635d30c66279772 (diff)
locks: fix possible infinite loop in fcntl(F_SETLKW) over nfs
upstream commit: 19e729a928172103e101ffd0829fd13e68c13f78 Miklos Szeredi found the bug: "Basically what happens is that on the server nlm_fopen() calls nfsd_open() which returns -EACCES, to which nlm_fopen() returns NLM_LCK_DENIED. "On the client this will turn into a -EAGAIN (nlm_stat_to_errno()), which in will cause fcntl_setlk() to retry forever." So, for example, opening a file on an nfs filesystem, changing permissions to forbid further access, then trying to lock the file, could result in an infinite loop. And Trond Myklebust identified the culprit, from Marc Eshel and I: 7723ec9777d9832849b76475b1a21a2872a40d20 "locks: factor out generic/filesystem switch from setlock code" That commit claimed to just be reshuffling code, but actually introduced a behavioral change by calling the lock method repeatedly as long as it returned -EAGAIN. We assumed this would be safe, since we assumed a lock of type SETLKW would only return with either success or an error other than -EAGAIN. However, nfs does can in fact return -EAGAIN in this situation, and independently of whether that behavior is correct or not, we don't actually need this change, and it seems far safer not to depend on such assumptions about the filesystem's ->lock method. Therefore, revert the problematic part of the original commit. This leaves vfs_lock_file() and its other callers unchanged, while returning fcntl_setlk and fcntl_setlk64 to their former behavior. Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu> Tested-by: Miklos Szeredi <mszeredi@suse.cz> Cc: Trond Myklebust <trond.myklebust@fys.uio.no> Cc: Marc Eshel <eshel@almaden.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Chris Wright <chrisw@sous-sol.org>
-rw-r--r--fs/locks.c48
1 files changed, 28 insertions, 20 deletions
diff --git a/fs/locks.c b/fs/locks.c
index 8b8388eca05e..2fd29d929afb 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1805,17 +1805,21 @@ again:
if (error)
goto out;
- for (;;) {
- error = vfs_lock_file(filp, cmd, file_lock, NULL);
- if (error != -EAGAIN || cmd == F_SETLK)
- break;
- error = wait_event_interruptible(file_lock->fl_wait,
- !file_lock->fl_next);
- if (!error)
- continue;
+ if (filp->f_op && filp->f_op->lock != NULL)
+ error = filp->f_op->lock(filp, cmd, file_lock);
+ else {
+ for (;;) {
+ error = posix_lock_file(filp, file_lock, NULL);
+ if (error != -EAGAIN || cmd == F_SETLK)
+ break;
+ error = wait_event_interruptible(file_lock->fl_wait,
+ !file_lock->fl_next);
+ if (!error)
+ continue;
- locks_delete_block(file_lock);
- break;
+ locks_delete_block(file_lock);
+ break;
+ }
}
/*
@@ -1929,17 +1933,21 @@ again:
if (error)
goto out;
- for (;;) {
- error = vfs_lock_file(filp, cmd, file_lock, NULL);
- if (error != -EAGAIN || cmd == F_SETLK64)
- break;
- error = wait_event_interruptible(file_lock->fl_wait,
- !file_lock->fl_next);
- if (!error)
- continue;
+ if (filp->f_op && filp->f_op->lock != NULL)
+ error = filp->f_op->lock(filp, cmd, file_lock);
+ else {
+ for (;;) {
+ error = posix_lock_file(filp, file_lock, NULL);
+ if (error != -EAGAIN || cmd == F_SETLK64)
+ break;
+ error = wait_event_interruptible(file_lock->fl_wait,
+ !file_lock->fl_next);
+ if (!error)
+ continue;
- locks_delete_block(file_lock);
- break;
+ locks_delete_block(file_lock);
+ break;
+ }
}
/*