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fs: Check for invalid i_uid in may_follow_link()

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[ Upstream commit 2d7f9e2ad35e4e7a3086231f19bfab33c6a8a64a ]

Filesystem uids which don't map into a user namespace may result
in inode->i_uid being INVALID_UID. A symlink and its parent
could have different owners in the filesystem can both get
mapped to INVALID_UID, which may result in following a symlink
when this would not have otherwise been permitted when protected
symlinks are enabled.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Seth Forshee 2016-08-30 00:35:00 -04:00 • committed by Greg Kroah-Hartman
parent 917f84b8df
commit 6a90aa4406
1 changed files with 3 additions and 1 deletions
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4
fs/namei.c
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@ -887,6 +887,7 @@ static inline int may_follow_link(struct nameidata *nd)
{ {
const struct inode *inode; const struct inode *inode;
const struct inode *parent; const struct inode *parent;
kuid_t puid;
if (!sysctl_protected_symlinks) if (!sysctl_protected_symlinks)
return 0; return 0;
@ -902,7 +903,8 @@ static inline int may_follow_link(struct nameidata *nd)
return 0; return 0;
/* Allowed if parent directory and link owner match. */ /* Allowed if parent directory and link owner match. */
if (uid_eq(parent->i_uid, inode->i_uid)) puid = parent->i_uid;
if (uid_valid(puid) && uid_eq(puid, inode->i_uid))
return 0; return 0;
if (nd->flags & LOOKUP_RCU) if (nd->flags & LOOKUP_RCU)