Messages in this thread Patch in this message | | | From | Luis Henriques <> | Subject | [PATCH 013/102] Nest rename_lock inside vfsmount_lock | Date | Mon, 8 Apr 2013 10:49:28 +0100 |
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3.5.7.10 -stable review patch. If anyone has any objections, please let me know.
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From: Al Viro <viro@zeniv.linux.org.uk>
commit 7ea600b5314529f9d1b9d6d3c41cb26fce6a7a4a upstream.
... 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> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> [ luis: adjust context ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- fs/dcache.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c index 1845c46..458ec45 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2579,7 +2579,6 @@ 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; @@ -2609,8 +2608,6 @@ 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: @@ -2627,7 +2624,7 @@ global_root: error = prepend(buffer, buflen, "/", 1); if (!error) error = real_mount(vfsmnt)->mnt_ns ? 1 : 2; - goto out; + return error; } /** @@ -2654,9 +2651,11 @@ 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); @@ -2673,9 +2672,11 @@ 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; @@ -2739,11 +2740,13 @@ 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; } @@ -2898,6 +2901,7 @@ 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; @@ -2907,6 +2911,7 @@ 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; @@ -2927,6 +2932,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size) } } else { write_sequnlock(&rename_lock); + br_read_unlock(&vfsmount_lock); } out: -- 1.8.1.2
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