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authorDavidlohr Bueso <dave@stgolabs.net>2018-04-10 16:35:23 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-11 10:28:37 -0700
commitc21a6970ae727839a2f300cd8dd957de0d0238c3 (patch)
tree2fb730ab2d08213bf196c4a9a56d49a6e2f664f7 /security
parentedc41b3c5489996e4c1ec820bf102660bf745c45 (diff)
downloadlinux-stericsson-c21a6970ae727839a2f300cd8dd957de0d0238c3.tar.gz
ipc/shm: introduce shmctl(SHM_STAT_ANY)
Patch series "sysvipc: introduce STAT_ANY commands", v2. The following patches adds the discussed (see [1]) new command for shm as well as for sems and msq as they are subject to the same discrepancies for ipc object permission checks between the syscall and via procfs. These new commands are justified in that (1) we are stuck with this semantics as changing syscall and procfs can break userland; and (2) some users can benefit from performance (for large amounts of shm segments, for example) from not having to parse the procfs interface. Once merged, I will submit the necesary manpage updates. But I'm thinking something like: : diff --git a/man2/shmctl.2 b/man2/shmctl.2 : index 7bb503999941..bb00bbe21a57 100644 : --- a/man2/shmctl.2 : +++ b/man2/shmctl.2 : @@ -41,6 +41,7 @@ : .\" 2005-04-25, mtk -- noted aberrant Linux behavior w.r.t. new : .\" attaches to a segment that has already been marked for deletion. : .\" 2005-08-02, mtk: Added IPC_INFO, SHM_INFO, SHM_STAT descriptions. : +.\" 2018-02-13, dbueso: Added SHM_STAT_ANY description. : .\" : .TH SHMCTL 2 2017-09-15 "Linux" "Linux Programmer's Manual" : .SH NAME : @@ -242,6 +243,18 @@ However, the : argument is not a segment identifier, but instead an index into : the kernel's internal array that maintains information about : all shared memory segments on the system. : +.TP : +.BR SHM_STAT_ANY " (Linux-specific)" : +Return a : +.I shmid_ds : +structure as for : +.BR SHM_STAT . : +However, the : +.I shm_perm.mode : +is not checked for read access for : +.IR shmid , : +resembing the behaviour of : +/proc/sysvipc/shm. : .PP : The caller can prevent or allow swapping of a shared : memory segment with the following \fIcmd\fP values: : @@ -287,7 +300,7 @@ operation returns the index of the highest used entry in the : kernel's internal array recording information about all : shared memory segments. : (This information can be used with repeated : -.B SHM_STAT : +.B SHM_STAT/SHM_STAT_ANY : operations to obtain information about all shared memory segments : on the system.) : A successful : @@ -328,7 +341,7 @@ isn't accessible. : \fIshmid\fP is not a valid identifier, or \fIcmd\fP : is not a valid command. : Or: for a : -.B SHM_STAT : +.B SHM_STAT/SHM_STAT_ANY : operation, the index value specified in : .I shmid : referred to an array slot that is currently unused. This patch (of 3): There is a permission discrepancy when consulting shm ipc object metadata between /proc/sysvipc/shm (0444) and the SHM_STAT shmctl command. The later does permission checks for the object vs S_IRUGO. As such there can be cases where EACCESS is returned via syscall but the info is displayed anyways in the procfs files. While this might have security implications via info leaking (albeit no writing to the shm metadata), this behavior goes way back and showing all the objects regardless of the permissions was most likely an overlook - so we are stuck with it. Furthermore, modifying either the syscall or the procfs file can cause userspace programs to break (ie ipcs). Some applications require getting the procfs info (without root privileges) and can be rather slow in comparison with a syscall -- up to 500x in some reported cases. This patch introduces a new SHM_STAT_ANY command such that the shm ipc object permissions are ignored, and only audited instead. In addition, I've left the lsm security hook checks in place, as if some policy can block the call, then the user has no other choice than just parsing the procfs file. [1] https://lkml.org/lkml/2017/12/19/220 Link: http://lkml.kernel.org/r/20180215162458.10059-2-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Kees Cook <keescook@chromium.org> Cc: Robert Kettler <robert.kettler@outlook.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'security')
-rw-r--r--security/selinux/hooks.c1
-rw-r--r--security/smack/smack_lsm.c1
2 files changed, 2 insertions, 0 deletions
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 1eeb70e439d7..1287013f747d 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6157,6 +6157,7 @@ static int selinux_shm_shmctl(struct kern_ipc_perm *shp, int cmd)
SECCLASS_SYSTEM, SYSTEM__IPC_INFO, NULL);
case IPC_STAT:
case SHM_STAT:
+ case SHM_STAT_ANY:
perms = SHM__GETATTR | SHM__ASSOCIATE;
break;
case IPC_SET:
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 73549007bf9e..0daab3019023 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3046,6 +3046,7 @@ static int smack_shm_shmctl(struct kern_ipc_perm *isp, int cmd)
switch (cmd) {
case IPC_STAT:
case SHM_STAT:
+ case SHM_STAT_ANY:
may = MAY_READ;
break;
case IPC_SET: