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authorJ. Bruce Fields <bfields@citi.umich.edu>2008-04-14 15:03:02 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-14 12:22:14 -0700
commit19e729a928172103e101ffd0829fd13e68c13f78 (patch)
tree5d3492a6dd2191abebe27a8d59e181398375e9c8 /fs/locks.c
parenta985aabe4d7a720b109c2b63549f8641676a9c88 (diff)
locks: fix possible infinite loop in fcntl(F_SETLKW) over nfs
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>
Diffstat (limited to 'fs/locks.c')
-rw-r--r--fs/locks.c48
1 files changed, 28 insertions, 20 deletions
diff --git a/fs/locks.c b/fs/locks.c
index d83fab1b77b5..43c0af21a0c5 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1801,17 +1801,21 @@ 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;
+ }
}
/*
@@ -1925,17 +1929,21 @@ 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;
+ }
}
/*

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