tjh.dev / kernel
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CRED: Fix BUG() upon security_cred_alloc_blank() failure

In cred_alloc_blank() since 2.6.32, abort_creds(new) is called with
new->security == NULL and new->magic == 0 when security_cred_alloc_blank()
returns an error. As a result, BUG() will be triggered if SELinux is enabled
or CONFIG_DEBUG_CREDENTIALS=y.

If CONFIG_DEBUG_CREDENTIALS=y, BUG() is called from __invalid_creds() because
cred->magic == 0. Failing that, BUG() is called from selinux_cred_free()
because selinux_cred_free() is not expecting cred->security == NULL. This does
not affect smack_cred_free(), tomoyo_cred_free() or apparmor_cred_free().

Fix these bugs by

(1) Set new->magic before calling security_cred_alloc_blank().

(2) Handle null cred->security in creds_are_invalid() and selinux_cred_free().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

authored by

Tetsuo Handa and committed by
Linus Torvalds 2edeaa34 257a65d7

+13 -5
+8 -4
kernel/cred.c
··· 252 252 #endif 253 253 254 254 atomic_set(&new->usage, 1); 255 + #ifdef CONFIG_DEBUG_CREDENTIALS 256 + new->magic = CRED_MAGIC; 257 + #endif 255 258 256 259 if (security_cred_alloc_blank(new, GFP_KERNEL) < 0) 257 260 goto error; 258 261 259 - #ifdef CONFIG_DEBUG_CREDENTIALS 260 - new->magic = CRED_MAGIC; 261 - #endif 262 262 return new; 263 263 264 264 error: ··· 748 748 if (cred->magic != CRED_MAGIC) 749 749 return true; 750 750 #ifdef CONFIG_SECURITY_SELINUX 751 - if (selinux_is_enabled()) { 751 + /* 752 + * cred->security == NULL if security_cred_alloc_blank() or 753 + * security_prepare_creds() returned an error. 754 + */ 755 + if (selinux_is_enabled() && cred->security) { 752 756 if ((unsigned long) cred->security < PAGE_SIZE) 753 757 return true; 754 758 if ((*(u32 *)cred->security & 0xffffff00) ==
+5 -1
security/selinux/hooks.c
··· 3198 3198 { 3199 3199 struct task_security_struct *tsec = cred->security; 3200 3200 3201 - BUG_ON((unsigned long) cred->security < PAGE_SIZE); 3201 + /* 3202 + * cred->security == NULL if security_cred_alloc_blank() or 3203 + * security_prepare_creds() returned an error. 3204 + */ 3205 + BUG_ON(cred->security && (unsigned long) cred->security < PAGE_SIZE); 3202 3206 cred->security = (void *) 0x7UL; 3203 3207 kfree(tsec); 3204 3208 }