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Eric Biggers dc32b5c3e6 capabilities: fix buffer overread on very short xattr 
If userspace attempted to set a "security.capability" xattr shorter than
4 bytes (e.g. 'setfattr -n security.capability -v x file'), then
cap_convert_nscap() read past the end of the buffer containing the xattr
value because it accessed the ->magic_etc field without verifying that
the xattr value is long enough to contain that field.

Fix it by validating the xattr value size first.

This bug was found using syzkaller with KASAN.  The KASAN report was as
follows (cleaned up slightly):

    BUG: KASAN: slab-out-of-bounds in cap_convert_nscap+0x514/0x630 security/commoncap.c:498
    Read of size 4 at addr ffff88002d8741c0 by task syz-executor1/2852

    CPU: 0 PID: 2852 Comm: syz-executor1 Not tainted 4.15.0-rc6-00200-gcc0aac99d977 #253
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-20171110_100015-anatol 04/01/2014
    Call Trace:
     __dump_stack lib/dump_stack.c:17 [inline]
     dump_stack+0xe3/0x195 lib/dump_stack.c:53
     print_address_description+0x73/0x260 mm/kasan/report.c:252
     kasan_report_error mm/kasan/report.c:351 [inline]
     kasan_report+0x235/0x350 mm/kasan/report.c:409
     cap_convert_nscap+0x514/0x630 security/commoncap.c:498
     setxattr+0x2bd/0x350 fs/xattr.c:446
     path_setxattr+0x168/0x1b0 fs/xattr.c:472
     SYSC_setxattr fs/xattr.c:487 [inline]
     SyS_setxattr+0x36/0x50 fs/xattr.c:483
     entry_SYSCALL_64_fastpath+0x18/0x85

Fixes: 8db6c34f1d ("Introduce v3 namespaced file capabilities")
Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
2018-01-02 20:49:13 +11:00
..
apparmor bug fixes: 2017-11-30 18:56:41 -05:00
integrity ima: do not update security.ima if appraisal status is not INTEGRITY_PASS 2017-11-20 08:23:10 +11:00
keys KEYS: reject NULL restriction string when type is specified 2017-12-08 15:13:29 +00:00
loadpin security: mark LSM hooks as __ro_after_init 2017-03-06 11:00:15 +11:00
selinux selinux/stable-4.15 PR 20171113 2017-11-15 13:32:56 -08:00
smack Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2017-11-13 10:30:44 -08:00
tomoyo Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2017-11-13 10:30:44 -08:00
yama doc: ReSTify Yama.txt 2017-05-18 10:33:04 -06:00
commoncap.c capabilities: fix buffer overread on very short xattr 2018-01-02 20:49:13 +11:00
device_cgroup.c device_cgroup: prepare code for bpf-based device controller 2017-11-05 23:26:51 +09:00
inode.c securityfs: add the ability to support symlinks 2017-06-08 12:51:43 -07:00
Kconfig x86/mm/pti: Add Kconfig 2017-12-23 21:13:01 +01:00
lsm_audit.c lsm_audit: update my email address 2017-08-17 15:33:39 -04:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
min_addr.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
security.c security: bpf: Add LSM hooks for bpf object related syscall 2017-10-20 13:32:59 +01:00