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KEYS: restrict /proc/keys by credentials at open time

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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 34dbbcdbf6 ("Make file credentials available to the
seqfile interfaces") we can finally fix it.  So let's do it.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
Eric Biggers 2017-09-18 11:38:29 -07:00 committed by David Howells
parent 8f674565d4
commit 4aa68e07d8
1 changed files with 2 additions and 6 deletions
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8
security/keys/proc.c
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@ -187,7 +187,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
struct keyring_search_context ctx = { struct keyring_search_context ctx = {
.index_key.type = key->type, .index_key.type = key->type,
.index_key.description = key->description, .index_key.description = key->description,
.cred = current_cred(), .cred = m->file->f_cred,
.match_data.cmp = lookup_user_key_possessed, .match_data.cmp = lookup_user_key_possessed,
.match_data.raw_data = key, .match_data.raw_data = key,
.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT, .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 /* check whether the current task is allowed to view the key */
* non-possession)
* - the caller holds a spinlock, and thus the RCU read lock, making our
* access to __current_cred() safe
*/
rc = key_task_permission(key_ref, ctx.cred, KEY_NEED_VIEW); rc = key_task_permission(key_ref, ctx.cred, KEY_NEED_VIEW);
if (rc < 0) if (rc < 0)
return 0; return 0;