Messages in this thread | | | Subject | Re: [PATCH] Change task_struct->comm to use RCU. | From | Tetsuo Handa <> | Date | Sat, 8 Mar 2014 21:43:36 +0900 |
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Richard Guy Briggs wrote: > > > > Likewise, audit_log_untrustedstring(ab, current->comm) is racy. > > > > If task->comm was "Hello Linux" until audit_string_contains_control() in > > > > audit_log_n_untrustedstring() returns false, and becomes "Penguin" before > > > > memcpy() in audit_log_n_string() is called, memcpy() will emit "Penguin\0nux" > > > > into the audit log, which results in loss of information (e.g. SELinux > > > > context) due to the unexpected '\0' byte. > > > > > > I expect the audit people don't like this? Also, how do audit and the > > > LSM crap things interact? I thought they were both different piles of > > > ignorable goo? > > > > I think the audit people do not like loss of information. Some of LSM modules > > are using audit subsystem for recording security related events. An example is > > shown later. > > This is true, however since comm it untrusted because it can be modified > by the user audit doesn't trust it anyways, so who cares?
Excuse me, but did you understand this side effect correctly?
# ln /bin/true /tmp/printable-comm # auditctl -a exit,always -S execve -F path=/tmp/printable-comm # /tmp/printable-comm # cat /var/log/audit/audit.log
If we didn't race, everything is fine.
---------- An audit log without race ---------- type=SYSCALL msg=audit(1394281486.738:62): arch=40000003 syscall=11 success=yes exit=0 a0=8589c48 a1=85a6620 a2=858e4a0 a3=85a6620 items=2 ppid=1747 pid=2657 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts1 ses=2 comm="printable-comm" exe="/tmp/printable-comm" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=(null) type=EXECVE msg=audit(1394281486.738:62): argc=1 a0="/tmp/printable-comm" type=CWD msg=audit(1394281486.738:62): cwd="/root" type=PATH msg=audit(1394281486.738:62): item=0 name="/tmp/printable-comm" inode=1970955 dev=08:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:bin_t:s0 nametype=NORMAL type=PATH msg=audit(1394281486.738:62): item=1 name=(null) inode=2360187 dev=08:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:ld_so_t:s0 nametype=NORMAL ---------- An audit log without race ----------
But if we raced (you can use a (dangerous) SystemTap script shown below for emulating this race condition
# stap -g -e ' function rewrite_comm(str:long) %{ strlcpy((char *) (long) STAP_ARG_str, "truncated", sizeof(current->comm)); %} probe kernel.function("audit_log_n_string") { if ($ab && $slen == 14 && kernel_string($string) == "printable-comm") { rewrite_comm($string); printf("<%s>\n", kernel_string($string)) }; } '
), you can see that fields after comm= (e.g. exe= subj= key= ) are missing.
---------- An audit log with race ---------- type=SYSCALL msg=audit(1394281498.566:63): arch=40000003 syscall=11 success=yes exit=0 a0=858c9c8 a1=85a6620 a2=858e4a0 a3=85a6620 items=2 ppid=1747 pid=2662 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts1 ses=2 comm="truncated type=EXECVE msg=audit(1394281498.566:63): argc=1 a0="/tmp/printable-comm" type=CWD msg=audit(1394281498.566:63): cwd="/root" type=PATH msg=audit(1394281498.566:63): item=0 name="/tmp/printable-comm" inode=1970955 dev=08:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:bin_t:s0 nametype=NORMAL type=PATH msg=audit(1394281498.566:63): item=1 name=(null) inode=2360187 dev=08:01 mode=0100755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:ld_so_t:s0 nametype=NORMAL ---------- An audit log with race ----------
Even if you don't trust the comm= field, it is annoying for me that fields after comm= are missing in the audit log.
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