From: Eric Biggers <ebiggers@xxxxxxxxxx>
commit 4aa68e07d845562561f5e73c04aa521376e95252 upstream
When checking for permission to view keys whilst reading from
/proc/keys, we should use the credentials with which the /proc/keys file
was opened. This is because, in a classic type of exploit, it can be
possible to bypass checks for the *current* credentials by passing the
file descriptor to a suid program.
Following commit 34dbbcdbf633 ("Make file credentials available to the
seqfile interfaces") we can finally fix it. So let's do it.
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Zubin Mithra <zsm@xxxxxxxxxxxx>
---
* A test confirmed that when reading from a file descriptor
corresponding to /proc/keys the permissions for the reader were being
used instead of the permissions of the user who opened the file.
This patch is required for 4.4.y as well; however, the original patch
will apply cleanly there. I'll send a separate request for the same.
security/keys/proc.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/security/keys/proc.c b/security/keys/proc.c
index ec493ddadd111..f2c7e090a66d7 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -187,7 +187,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
struct keyring_search_context ctx = {
.index_key = key->index_key,
- .cred = current_cred(),
+ .cred = m->file->f_cred,
.match_data.cmp = lookup_user_key_possessed,
.match_data.raw_data = key,
.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
@@ -207,11 +207,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
}
}
- /* check whether the current task is allowed to view the key (assuming
- * non-possession)
- * - the caller holds a spinlock, and thus the RCU read lock, making our
- * access to __current_cred() safe
- */
+ /* check whether the current task is allowed to view the key */
rc = key_task_permission(key_ref, ctx.cred, KEY_NEED_VIEW);
if (rc < 0)
return 0;
--
2.21.0.360.g471c308f928-goog
