[PATCH v3 102/110] namei: make may_follow_link() safe in RCU mode

From: Al Viro
Date: Mon May 11 2015 - 14:13:26 EST

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

We *can't* call that audit garbage in RCU mode - it's doing a weird
mix of allocations (GFP_NOFS, immediately followed by GFP_KERNEL)
and I'm not touching that... thing again.

So if this security sclero^Whardening feature gets triggered when
we are in RCU mode, tough - we'll fail with -ECHILD and have
everything restarted in non-RCU mode. Only to hit the same test
and fail, this time with EACCES and with (oh, rapture) an audit spew

Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
fs/namei.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 998c3c2..20bf494 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -794,6 +794,9 @@ static inline int may_follow_link(struct nameidata *nd)
if (uid_eq(parent->i_uid, inode->i_uid))
return 0;

+ if (nd->flags & LOOKUP_RCU)
+ return -ECHILD;
audit_log_link_denied("follow_link", &nd->stack[0].link);
return -EACCES;

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