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authorAl Viro <viro@zeniv.linux.org.uk>2014-04-19 12:30:58 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2014-04-19 12:30:58 -0400
commit22213318af7ae265bc6cd8aef2febbc2d69a2440 (patch)
treebb9b6c5e25909555f5243d8983d07c96cfeb08a9
parentc9eaa447e77efe77b7fa4c953bd62de8297fd6c5 (diff)
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fix races between __d_instantiate() and checks of dentry flags
in non-lazy walk we need to be careful about dentry switching from negative to positive - both ->d_flags and ->d_inode are updated, and in some places we might see only one store. The cases where dentry has been obtained by dcache lookup with ->i_mutex held on parent are safe - ->d_lock and ->i_mutex provide all the barriers we need. However, there are several places where we run into trouble: * do_last() fetches ->d_inode, then checks ->d_flags and assumes that inode won't be NULL unless d_is_negative() is true. Race with e.g. creat() - we might have fetched the old value of ->d_inode (still NULL) and new value of ->d_flags (already not DCACHE_MISS_TYPE). Lin Ming has observed and reported the resulting oops. * a bunch of places checks ->d_inode for being non-NULL, then checks ->d_flags for "is it a symlink". Race with symlink(2) in case if our CPU sees ->d_inode update first - we see non-NULL there, but ->d_flags still contains DCACHE_MISS_TYPE instead of DCACHE_SYMLINK_TYPE. Result: false negative on "should we follow link here?", with subsequent unpleasantness. Cc: stable@vger.kernel.org # 3.13 and 3.14 need that one Reported-and-tested-by: Lin Ming <minggr@gmail.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/dcache.c3
-rw-r--r--fs/namei.c6
2 files changed, 4 insertions, 5 deletions
diff --git a/fs/dcache.c b/fs/dcache.c
index 40707d88a945..494a9def5dce 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1647,8 +1647,7 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode)
unsigned add_flags = d_flags_for_inode(inode);
spin_lock(&dentry->d_lock);
- dentry->d_flags &= ~DCACHE_ENTRY_TYPE;
- dentry->d_flags |= add_flags;
+ __d_set_type(dentry, add_flags);
if (inode)
hlist_add_head(&dentry->d_alias, &inode->i_dentry);
dentry->d_inode = inode;
diff --git a/fs/namei.c b/fs/namei.c
index c6157c894fce..80168273396b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1542,7 +1542,7 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
inode = path->dentry->d_inode;
}
err = -ENOENT;
- if (!inode)
+ if (!inode || d_is_negative(path->dentry))
goto out_path_put;
if (should_follow_link(path->dentry, follow)) {
@@ -2249,7 +2249,7 @@ mountpoint_last(struct nameidata *nd, struct path *path)
mutex_unlock(&dir->d_inode->i_mutex);
done:
- if (!dentry->d_inode) {
+ if (!dentry->d_inode || d_is_negative(dentry)) {
error = -ENOENT;
dput(dentry);
goto out;
@@ -2994,7 +2994,7 @@ retry_lookup:
finish_lookup:
/* we _can_ be in RCU mode here */
error = -ENOENT;
- if (d_is_negative(path->dentry)) {
+ if (!inode || d_is_negative(path->dentry)) {
path_to_nameidata(path, nd);
goto out;
}