Re: [PATCH] smack: fix possible use after frees in task_security() callers
From: Casey Schaufler
Date: Wed Jan 14 2015 - 02:13:03 EST
On 1/13/2015 7:52 AM, Andrey Ryabinin wrote:
> We hit use after free on dereferncing pointer to task_smack struct in
> smk_of_task() called from smack_task_to_inode().
>
> task_security() macro uses task_cred_xxx() to get pointer to the task_smack.
> task_cred_xxx() could be used only for non-pointer members of task's
> credentials. It cannot be used for pointer members since what they point
> to may disapper after dropping RCU read lock.
>
> Mainly task_security() used this way:
> smk_of_task(task_security(p))
>
> Intead of this introduce function smk_of_task_struct() which
> takes task_struct as argument and returns pointer to smk_known struct
> and do this under RCU read lock.
> Bogus task_security() macro is not used anymore, so remove it.
>
> KASan's report for this:
>
> AddressSanitizer: use after free in smack_task_to_inode+0x50/0x70 at addr c4635600
> =============================================================================
> BUG kmalloc-64 (Tainted: PO): kasan error
> -----------------------------------------------------------------------------
>
> Disabling lock debugging due to kernel taint
> INFO: Allocated in new_task_smack+0x44/0xd8 age=39 cpu=0 pid=1866
> kmem_cache_alloc_trace+0x88/0x1bc
> new_task_smack+0x44/0xd8
> smack_cred_prepare+0x48/0x21c
> security_prepare_creds+0x44/0x4c
> prepare_creds+0xdc/0x110
> smack_setprocattr+0x104/0x150
> security_setprocattr+0x4c/0x54
> proc_pid_attr_write+0x12c/0x194
> vfs_write+0x1b0/0x370
> SyS_write+0x5c/0x94
> ret_fast_syscall+0x0/0x48
> INFO: Freed in smack_cred_free+0xc4/0xd0 age=27 cpu=0 pid=1564
> kfree+0x270/0x290
> smack_cred_free+0xc4/0xd0
> security_cred_free+0x34/0x3c
> put_cred_rcu+0x58/0xcc
> rcu_process_callbacks+0x738/0x998
> __do_softirq+0x264/0x4cc
> do_softirq+0x94/0xf4
> irq_exit+0xbc/0x120
> handle_IRQ+0x104/0x134
> gic_handle_irq+0x70/0xac
> __irq_svc+0x44/0x78
> _raw_spin_unlock+0x18/0x48
> sync_inodes_sb+0x17c/0x1d8
> sync_filesystem+0xac/0xfc
> vdfs_file_fsync+0x90/0xc0
> vfs_fsync_range+0x74/0x7c
> INFO: Slab 0xd3b23f50 objects=32 used=31 fp=0xc4635600 flags=0x4080
> INFO: Object 0xc4635600 @offset=5632 fp=0x (null)
>
> Bytes b4 c46355f0: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
> Object c4635600: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> Object c4635610: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> Object c4635620: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> Object c4635630: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk.
> Redzone c4635640: bb bb bb bb ....
> Padding c46356e8: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZZZZZZZZZ
> Padding c46356f8: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
> CPU: 5 PID: 834 Comm: launchpad_prelo Tainted: PBO 3.10.30 #1
> Backtrace:
> [<c00233a4>] (dump_backtrace+0x0/0x158) from [<c0023dec>] (show_stack+0x20/0x24)
> r7:c4634010 r6:d3b23f50 r5:c4635600 r4:d1002140
> [<c0023dcc>] (show_stack+0x0/0x24) from [<c06d6d7c>] (dump_stack+0x20/0x28)
> [<c06d6d5c>] (dump_stack+0x0/0x28) from [<c01c1d50>] (print_trailer+0x124/0x144)
> [<c01c1c2c>] (print_trailer+0x0/0x144) from [<c01c1e88>] (object_err+0x3c/0x44)
> r7:c4635600 r6:d1002140 r5:d3b23f50 r4:c4635600
> [<c01c1e4c>] (object_err+0x0/0x44) from [<c01cac18>] (kasan_report_error+0x2b8/0x538)
> r6:d1002140 r5:d3b23f50 r4:c6429cf8 r3:c09e1aa7
> [<c01ca960>] (kasan_report_error+0x0/0x538) from [<c01c9430>] (__asan_load4+0xd4/0xf8)
> [<c01c935c>] (__asan_load4+0x0/0xf8) from [<c031e168>] (smack_task_to_inode+0x50/0x70)
> r5:c4635600 r4:ca9da000
> [<c031e118>] (smack_task_to_inode+0x0/0x70) from [<c031af64>] (security_task_to_inode+0x3c/0x44)
> r5:cca25e80 r4:c0ba9780
> [<c031af28>] (security_task_to_inode+0x0/0x44) from [<c023d614>] (pid_revalidate+0x124/0x178)
> r6:00000000 r5:cca25e80 r4:cbabe3c0 r3:00008124
> [<c023d4f0>] (pid_revalidate+0x0/0x178) from [<c01db98c>] (lookup_fast+0x35c/0x43y4)
> r9:c6429efc r8:00000101 r7:c079d940 r6:c6429e90 r5:c6429ed8 r4:c83c4148
> [<c01db630>] (lookup_fast+0x0/0x434) from [<c01deec8>] (do_last.isra.24+0x1c0/0x1108)
> [<c01ded08>] (do_last.isra.24+0x0/0x1108) from [<c01dff04>] (path_openat.isra.25+0xf4/0x648)
> [<c01dfe10>] (path_openat.isra.25+0x0/0x648) from [<c01e1458>] (do_filp_open+0x3c/0x88)
> [<c01e141c>] (do_filp_open+0x0/0x88) from [<c01ccb28>] (do_sys_open+0xf0/0x198)
> r7:00000001 r6:c0ea2180 r5:0000000b r4:00000000
> [<c01cca38>] (do_sys_open+0x0/0x198) from [<c01ccc00>] (SyS_open+0x30/0x34)
> [<c01ccbd0>] (SyS_open+0x0/0x34) from [<c001db80>] (ret_fast_syscall+0x0/0x48)
> Read of size 4 by thread T834:
> Memory state around the buggy address:
> c4635380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> c4635400: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
> c4635480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> c4635500: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
> c4635580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >c4635600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> c4635680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> c4635700: 00 00 00 00 04 fc fc fc fc fc fc fc fc fc fc fc
> c4635780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> c4635800: 00 00 00 00 00 00 04 fc fc fc fc fc fc fc fc fc
> c4635880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
> Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
I'm away from my primary tools, but will accept this into my tree
in a few days. Thank you.
> ---
> security/smack/smack.h | 10 ++++++++++
> security/smack/smack_lsm.c | 24 +++++++++++++-----------
> 2 files changed, 23 insertions(+), 11 deletions(-)
>
> diff --git a/security/smack/smack.h b/security/smack/smack.h
> index b828a37..b48359c 100644
> --- a/security/smack/smack.h
> +++ b/security/smack/smack.h
> @@ -298,6 +298,16 @@ static inline struct smack_known *smk_of_task(const struct task_smack *tsp)
> return tsp->smk_task;
> }
>
> +static inline struct smack_known *smk_of_task_struct(const struct task_struct *t)
> +{
> + struct smack_known *skp;
> +
> + rcu_read_lock();
> + skp = smk_of_task(__task_cred(t)->security);
> + rcu_read_unlock();
> + return skp;
> +}
> +
> /*
> * Present a pointer to the forked smack label entry in an task blob.
> */
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index f1b17a4..a717877 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -43,8 +43,6 @@
> #include <linux/binfmts.h>
> #include "smack.h"
>
> -#define task_security(task) (task_cred_xxx((task), security))
> -
> #define TRANS_TRUE "TRUE"
> #define TRANS_TRUE_SIZE 4
>
> @@ -120,7 +118,7 @@ static int smk_bu_current(char *note, struct smack_known *oskp,
> static int smk_bu_task(struct task_struct *otp, int mode, int rc)
> {
> struct task_smack *tsp = current_security();
> - struct task_smack *otsp = task_security(otp);
> + struct smack_known *smk_task = smk_of_task_struct(otp);
> char acc[SMK_NUM_ACCESS_TYPE + 1];
>
> if (rc <= 0)
> @@ -128,7 +126,7 @@ static int smk_bu_task(struct task_struct *otp, int mode, int rc)
>
> smk_bu_mode(mode, acc);
> pr_info("Smack Bringup: (%s %s %s) %s to %s\n",
> - tsp->smk_task->smk_known, otsp->smk_task->smk_known, acc,
> + tsp->smk_task->smk_known, smk_task->smk_known, acc,
> current->comm, otp->comm);
> return 0;
> }
> @@ -345,7 +343,8 @@ static int smk_ptrace_rule_check(struct task_struct *tracer,
> saip = &ad;
> }
>
> - tsp = task_security(tracer);
> + rcu_read_lock();
> + tsp = __task_cred(tracer)->security;
> tracer_known = smk_of_task(tsp);
>
> if ((mode & PTRACE_MODE_ATTACH) &&
> @@ -365,11 +364,14 @@ static int smk_ptrace_rule_check(struct task_struct *tracer,
> tracee_known->smk_known,
> 0, rc, saip);
>
> + rcu_read_unlock();
> return rc;
> }
>
> /* In case of rule==SMACK_PTRACE_DEFAULT or mode==PTRACE_MODE_READ */
> rc = smk_tskacc(tsp, tracee_known, smk_ptrace_mode(mode), saip);
> +
> + rcu_read_unlock();
> return rc;
> }
>
> @@ -396,7 +398,7 @@ static int smack_ptrace_access_check(struct task_struct *ctp, unsigned int mode)
> if (rc != 0)
> return rc;
>
> - skp = smk_of_task(task_security(ctp));
> + skp = smk_of_task_struct(ctp);
>
> rc = smk_ptrace_rule_check(current, skp, mode, __func__);
> return rc;
> @@ -1826,7 +1828,7 @@ static int smk_curacc_on_task(struct task_struct *p, int access,
> const char *caller)
> {
> struct smk_audit_info ad;
> - struct smack_known *skp = smk_of_task(task_security(p));
> + struct smack_known *skp = smk_of_task_struct(p);
> int rc;
>
> smk_ad_init(&ad, caller, LSM_AUDIT_DATA_TASK);
> @@ -1879,7 +1881,7 @@ static int smack_task_getsid(struct task_struct *p)
> */
> static void smack_task_getsecid(struct task_struct *p, u32 *secid)
> {
> - struct smack_known *skp = smk_of_task(task_security(p));
> + struct smack_known *skp = smk_of_task_struct(p);
>
> *secid = skp->smk_secid;
> }
> @@ -1986,7 +1988,7 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
> {
> struct smk_audit_info ad;
> struct smack_known *skp;
> - struct smack_known *tkp = smk_of_task(task_security(p));
> + struct smack_known *tkp = smk_of_task_struct(p);
> int rc;
>
> smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
> @@ -2040,7 +2042,7 @@ static int smack_task_wait(struct task_struct *p)
> static void smack_task_to_inode(struct task_struct *p, struct inode *inode)
> {
> struct inode_smack *isp = inode->i_security;
> - struct smack_known *skp = smk_of_task(task_security(p));
> + struct smack_known *skp = smk_of_task_struct(p);
>
> isp->smk_inode = skp;
> }
> @@ -3200,7 +3202,7 @@ unlockandout:
> */
> static int smack_getprocattr(struct task_struct *p, char *name, char **value)
> {
> - struct smack_known *skp = smk_of_task(task_security(p));
> + struct smack_known *skp = smk_of_task_struct(p);
> char *cp;
> int slen;
>
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