The __do_follow_link function in fs/namei.c in the Linux kernel before 2.6.33 does not properly handle the last pathname component during use of certain filesystems, which allows local users to cause a denial of service (incorrect free operations and system crash) via an open system call. fix autofs/afs/etc. magic mountpoint breakage We end up trying to kfree() nd.last.name on open("/mnt/tmp", O_CREAT) if /mnt/tmp is an autofs direct mount. The reason is that nd.last_type is bogus here; we want LAST_BIND for everything of that kind and we get LAST_NORM left over from finding parent directory. So make sure that it *is* set properly; set to LAST_BIND before doing ->follow_link() - for normal symlinks it will be changed by __vfs_follow_link() and everything else needs it set that way. diff --git a/fs/namei.c b/fs/namei.c index b55440b..1b26b16 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -561,6 +561,7 @@ static __always_inline int __do_follow_link(struct path *path, struct nameidata dget(dentry); } mntget(path->mnt); + nd->last_type = LAST_BIND; cookie = dentry->d_inode->i_op->follow_link(dentry, nd); error = PTR_ERR(cookie); if (!IS_ERR(cookie)) { diff --git a/fs/proc/base.c b/fs/proc/base.c index 18d5cc6..e42bbd8 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1419,7 +1419,6 @@ static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd) goto out; error = PROC_I(inode)->op.proc_get_link(inode, &nd->path); - nd->last_type = LAST_BIND; out: return ERR_PTR(error); }