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author | Jeff Layton <jlayton@redhat.com> | 2014-02-03 12:13:06 -0500 |
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committer | Jeff Layton <jlayton@redhat.com> | 2014-03-31 08:24:42 -0400 |
commit | 24cbe7845ea50b636ab2218b9d648270ff55f148 (patch) | |
tree | 89769bf1271ff804c830d0ba7898294a5762b7a6 /include/linux/fs.h | |
parent | 18156e7e66e5147d2483382a1e3817d2401ca1a8 (diff) | |
download | op-kernel-dev-24cbe7845ea50b636ab2218b9d648270ff55f148.zip op-kernel-dev-24cbe7845ea50b636ab2218b9d648270ff55f148.tar.gz |
locks: close potential race between setlease and open
As Al Viro points out, there is an unlikely, but possible race between
opening a file and setting a lease on it. generic_add_lease is done with
the i_lock held, but the inode->i_flock check in break_lease is
lockless. It's possible for another task doing an open to do the entire
pathwalk and call break_lease between the point where generic_add_lease
checks for a conflicting open and adds the lease to the list. If this
occurs, we can end up with a lease set on the file with a conflicting
open.
To guard against that, check again for a conflicting open after adding
the lease to the i_flock list. If the above race occurs, then we can
simply unwind the lease setting and return -EAGAIN.
Because we take dentry references and acquire write access on the file
before calling break_lease, we know that if the i_flock list is empty
when the open caller goes to check it then the necessary refcounts have
already been incremented. Thus the additional check for a conflicting
open will see that there is one and the setlease call will fail.
Cc: Bruce Fields <bfields@fieldses.org>
Cc: David Howells <dhowells@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@fieldses.org>
Diffstat (limited to 'include/linux/fs.h')
-rw-r--r-- | include/linux/fs.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h index 09f553c..df84744 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1964,6 +1964,12 @@ static inline int locks_verify_truncate(struct inode *inode, static inline int break_lease(struct inode *inode, unsigned int mode) { + /* + * Since this check is lockless, we must ensure that any refcounts + * taken are done before checking inode->i_flock. Otherwise, we could + * end up racing with tasks trying to set a new lease on this file. + */ + smp_mb(); if (inode->i_flock) return __break_lease(inode, mode, FL_LEASE); return 0; |