diff options
| author | Al Viro <viro@zeniv.linux.org.uk> | 2013-03-26 18:25:57 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-03-26 18:25:57 -0400 |
| commit | 7ea600b5314529f9d1b9d6d3c41cb26fce6a7a4a (patch) | |
| tree | 8cc99c507999dcb7c35e973e22d79ae9a3ac8165 | |
| parent | 06ae43f34bcc07a0b6be8bf78a1c895bcd12c839 (diff) | |
Nest rename_lock inside vfsmount_lock
... lest we get livelocks between path_is_under() and d_path() and friends.
The thing is, wrt fairness lglocks are more similar to rwsems than to rwlocks;
it is possible to have thread B spin on attempt to take lock shared while thread
A is already holding it shared, if B is on lower-numbered CPU than A and there's
a thread C spinning on attempt to take the same lock exclusive.
As the result, we need consistent ordering between vfsmount_lock (lglock) and
rename_lock (seq_lock), even though everything that takes both is going to take
vfsmount_lock only shared.
Spotted-by: Brad Spengler <spender@grsecurity.net>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| -rw-r--r-- | fs/dcache.c | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index fbfae008ba4..e8bc3420d63 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2542,7 +2542,6 @@ static int prepend_path(const struct path *path, bool slash = false; int error = 0; - br_read_lock(&vfsmount_lock); while (dentry != root->dentry || vfsmnt != root->mnt) { struct dentry * parent; @@ -2572,8 +2571,6 @@ static int prepend_path(const struct path *path, if (!error && !slash) error = prepend(buffer, buflen, "/", 1); -out: - br_read_unlock(&vfsmount_lock); return error; global_root: @@ -2590,7 +2587,7 @@ global_root: error = prepend(buffer, buflen, "/", 1); if (!error) error = is_mounted(vfsmnt) ? 1 : 2; - goto out; + return error; } /** @@ -2617,9 +2614,11 @@ char *__d_path(const struct path *path, int error; prepend(&res, &buflen, "\0", 1); + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); error = prepend_path(path, root, &res, &buflen); write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error < 0) return ERR_PTR(error); @@ -2636,9 +2635,11 @@ char *d_absolute_path(const struct path *path, int error; prepend(&res, &buflen, "\0", 1); + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); error = prepend_path(path, &root, &res, &buflen); write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error > 1) error = -EINVAL; @@ -2702,11 +2703,13 @@ char *d_path(const struct path *path, char *buf, int buflen) return path->dentry->d_op->d_dname(path->dentry, buf, buflen); get_fs_root(current->fs, &root); + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); error = path_with_deleted(path, &root, &res, &buflen); + write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error < 0) res = ERR_PTR(error); - write_sequnlock(&rename_lock); path_put(&root); return res; } @@ -2830,6 +2833,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size) get_fs_root_and_pwd(current->fs, &root, &pwd); error = -ENOENT; + br_read_lock(&vfsmount_lock); write_seqlock(&rename_lock); if (!d_unlinked(pwd.dentry)) { unsigned long len; @@ -2839,6 +2843,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size) prepend(&cwd, &buflen, "\0", 1); error = prepend_path(&pwd, &root, &cwd, &buflen); write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); if (error < 0) goto out; @@ -2859,6 +2864,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size) } } else { write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); } out: |