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LINUX: Avoid symlink-y resolution limits

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Implementing the d_automount or follow_link function pointers for our
directories means that we can hit symlink resolution limits during
lookup, since we look like a "symlink". We can hit these limits pretty
easily if there are just too many directories in the lookup path.

Our pseudo-symlink directories cannot contribute to an infinite
resolution loop, since our destination is always an actual directory,
not a symlink that will result in more redirection. So, decrement the
total_link_count counter when our d_automount or follow_link code is
reached, so we do not contribute to hitting the max resolution limit.

Note that this is not related to recursive symlink lookup (link_count)
but only to the iterative symlink limit (total_link_count). Our
lookups are not recursive here, and we are not causing more recursive
lookups like a normal text-based symlink would do.

Reviewed-on: http://gerrit.openafs.org/8009
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 238b88624a)

Change-Id: Ib14ee9d160189da658f36578e21bd458e6e7832a
Reviewed-on: http://gerrit.openafs.org/8195
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
This commit is contained in:
Andrew Deason 2012-08-21 17:03:30 -05:00 committed by Derrick Brashear
parent 654b5c5509
commit 12fd096719
1 changed files with 15 additions and 0 deletions
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15
src/afs/LINUX/osi_vnodeops.c
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@ -1082,6 +1082,10 @@ afs_dentry_automount(struct path *path)
{
struct dentry *target;
/* avoid symlink resolution limits when resolving; we cannot contribute to
* an infinite symlink loop */
current->total_link_count--;
target = canonical_dentry(path->dentry->d_inode);
if (target == path->dentry) {
@ -2017,6 +2021,17 @@ afs_linux_dir_follow_link(struct dentry *dentry, struct nameidata *nd)
struct dentry **dpp;
struct dentry *target;
if (current->total_link_count > 0) {
/* avoid symlink resolution limits when resolving; we cannot contribute to
* an infinite symlink loop */
/* only do this for follow_link when total_link_count is positive to be
* on the safe side; there is at least one code path in the Linux
* kernel where it seems like it may be possible to get here without
* total_link_count getting incremented. it is not clear on how that
* path is actually reached, but guard against it just to be safe */
current->total_link_count--;
}
target = canonical_dentry(dentry->d_inode);
# ifdef STRUCT_NAMEIDATA_HAS_PATH