user/sven/linux.git/security/commoncap.c, branch v4.14.200

exec: Always set cap_ambient in cap_bprm_set_creds

2020-06-03T06:18:01Z

[ Upstream commit a4ae32c71fe90794127b32d26d7ad795813b502e ] An invariant of cap_bprm_set_creds is that every field in the new cred structure that cap_bprm_set_creds might set, needs to be set every time to ensure the fields does not get a stale value. The field cap_ambient is not set every time cap_bprm_set_creds is called, which means that if there is a suid or sgid script with an interpreter that has neither the suid nor the sgid bits set the interpreter should be able to accept ambient credentials. Unfortuantely because cap_ambient is not reset to it's original value the interpreter can not accept ambient credentials. Given that the ambient capability set is expected to be controlled by the caller, I don't think this is particularly serious. But it is definitely worth fixing so the code works correctly. I have tested to verify my reading of the code is correct and the interpreter of a sgid can receive ambient capabilities with this change and cannot receive ambient capabilities without this change. Cc: stable@vger.kernel.org Cc: Andy Lutomirski Fixes: 58319057b784 ("capabilities: ambient capabilities") Signed-off-by: "Eric W. Biederman" Signed-off-by: Sasha Levin

cap_inode_getsecurity: use d_find_any_alias() instead of d_find_alias()

2018-09-09T17:56:01Z

commit 355139a8dba446cc11a424cddbf7afebc3041ba1 upstream. The code in cap_inode_getsecurity(), introduced by commit 8db6c34f1dbc ("Introduce v3 namespaced file capabilities"), should use d_find_any_alias() instead of d_find_alias() do handle unhashed dentry correctly. This is needed, for example, if execveat() is called with an open but unlinked overlayfs file, because overlayfs unhashes dentry on unlink. This is a regression of real life application, first reported at https://www.spinics.net/lists/linux-unionfs/msg05363.html Below reproducer and setup can reproduce the case. const char* exec="echo"; const char *newargv[] = { "echo", "hello", NULL}; const char *newenviron[] = { NULL }; int fd, err; fd = open(exec, O_PATH); unlink(exec); err = syscall(322/*SYS_execveat*/, fd, "", newargv, newenviron, AT_EMPTY_PATH); if(err<0) fprintf(stderr, "execveat: %s\n", strerror(errno)); gcc compile into ~/test/a.out mount -t overlay -orw,lowerdir=/mnt/l,upperdir=/mnt/u,workdir=/mnt/w none /mnt/m cd /mnt/m cp /bin/echo . ~/test/a.out Expected result: hello Actually result: execveat: Invalid argument dmesg: Invalid argument reading file caps for /dev/fd/3 The 2nd reproducer and setup emulates similar case but for regular filesystem: const char* exec="echo"; int fd, err; char buf[256]; fd = open(exec, O_RDONLY); unlink(exec); err = fgetxattr(fd, "security.capability", buf, 256); if(err<0) fprintf(stderr, "fgetxattr: %s\n", strerror(errno)); gcc compile into ~/test_fgetxattr cd /tmp cp /bin/echo . ~/test_fgetxattr Result: fgetxattr: Invalid argument On regular filesystem, for example, ext4 read xattr from disk and return to execveat(), will not trigger this issue, however, the overlay attr handler pass real dentry to vfs_getxattr() will. This reproducer calls fgetxattr() with an unlinked fd, involkes vfs_getxattr() then reproduced the case that d_find_alias() in cap_inode_getsecurity() can't find the unlinked dentry. Suggested-by: Amir Goldstein Acked-by: Amir Goldstein Acked-by: Serge E. Hallyn Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Cc: # v4.14 Signed-off-by: Eddie Horng Signed-off-by: Eric W. Biederman Signed-off-by: Greg Kroah-Hartman

commoncap: Handle memory allocation failure.

2018-04-29T09:33:16Z

commit 1f5781725dcbb026438e77091c91a94f678c3522 upstream. syzbot is reporting NULL pointer dereference at xattr_getsecurity() [1], for cap_inode_getsecurity() is returning sizeof(struct vfs_cap_data) when memory allocation failed. Return -ENOMEM if memory allocation failed. [1] https://syzkaller.appspot.com/bug?id=a55ba438506fe68649a5f50d2d82d56b365e0107 Signed-off-by: Tetsuo Handa Fixes: 8db6c34f1dbc8e06 ("Introduce v3 namespaced file capabilities") Reported-by: syzbot Cc: stable # 4.14+ Acked-by: Serge E. Hallyn Acked-by: James Morris Signed-off-by: Eric W. Biederman Signed-off-by: Greg Kroah-Hartman

capabilities: fix buffer overread on very short xattr

2018-01-05T14:48:57Z

commit dc32b5c3e6e2ef29cef76d9ce1b92d394446150e upstream. 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: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Signed-off-by: Eric Biggers Reviewed-by: Serge Hallyn Signed-off-by: James Morris Signed-off-by: Greg Kroah-Hartman

commoncap: move assignment of fs_ns to avoid null pointer dereference

2017-10-19T02:09:33Z

The pointer fs_ns is assigned from inode->i_ib->s_user_ns before a null pointer check on inode, hence if inode is actually null we will get a null pointer dereference on this assignment. Fix this by only dereferencing inode after the null pointer check on inode. Detected by CoverityScan CID#1455328 ("Dereference before null check") Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Signed-off-by: Colin Ian King Cc: stable@vger.kernel.org Acked-by: Serge Hallyn Signed-off-by: James Morris

Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

2017-09-24T18:40:41Z

Pull misc security layer update from James Morris: "This is the remaining 'general' change in the security tree for v4.14, following the direct merging of SELinux (+ TOMOYO), AppArmor, and seccomp. That's everything now for the security tree except IMA, which will follow shortly (I've been traveling for the past week with patchy internet)" * 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: security: fix description of values returned by cap_inode_need_killpriv

security: fix description of values returned by cap_inode_need_killpriv

2017-09-24T04:15:41Z

cap_inode_need_killpriv returns 1 if security.capability exists and has a value and inode_killpriv() is required, 0 otherwise. Fix the description of the return value to reflect this. Signed-off-by: Stefan Berger Reviewed-by: Serge Hallyn Signed-off-by: James Morris

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2017-09-12T01:34:47Z

Pull namespace updates from Eric Biederman: "Life has been busy and I have not gotten half as much done this round as I would have liked. I delayed it so that a minor conflict resolution with the mips tree could spend a little time in linux-next before I sent this pull request. This includes two long delayed user namespace changes from Kirill Tkhai. It also includes a very useful change from Serge Hallyn that allows the security capability attribute to be used inside of user namespaces. The practical effect of this is people can now untar tarballs and install rpms in user namespaces. It had been suggested to generalize this and encode some of the namespace information information in the xattr name. Upon close inspection that makes the things that should be hard easy and the things that should be easy more expensive. Then there is my bugfix/cleanup for signal injection that removes the magic encoding of the siginfo union member from the kernel internal si_code. The mips folks reported the case where I had used FPE_FIXME me is impossible so I have remove FPE_FIXME from mips, while at the same time including a return statement in that case to keep gcc from complaining about unitialized variables. I almost finished the work to get make copy_siginfo_to_user a trivial copy to user. The code is available at: git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git neuter-copy_siginfo_to_user-v3 But I did not have time/energy to get the code posted and reviewed before the merge window opened. I was able to see that the security excuse for just copying fields that we know are initialized doesn't work in practice there are buggy initializations that don't initialize the proper fields in siginfo. So we still sometimes copy unitialized data to userspace" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: Introduce v3 namespaced file capabilities mips/signal: In force_fcr31_sig return in the impossible case signal: Remove kernel interal si_code magic fcntl: Don't use ambiguous SIG_POLL si_codes prctl: Allow local CAP_SYS_ADMIN changing exe_file security: Use user_namespace::level to avoid redundant iterations in cap_capable() userns,pidns: Verify the userns for new pid namespaces signal/testing: Don't look for __SI_FAULT in userspace signal/mips: Document a conflict with SI_USER with SIGFPE signal/sparc: Document a conflict with SI_USER with SIGFPE signal/ia64: Document a conflict with SI_USER with SIGFPE signal/alpha: Document a conflict with SI_USER for SIGTRAP

Introduce v3 namespaced file capabilities

2017-09-01T19:57:15Z

Root in a non-initial user ns cannot be trusted to write a traditional security.capability xattr. If it were allowed to do so, then any unprivileged user on the host could map his own uid to root in a private namespace, write the xattr, and execute the file with privilege on the host. However supporting file capabilities in a user namespace is very desirable. Not doing so means that any programs designed to run with limited privilege must continue to support other methods of gaining and dropping privilege. For instance a program installer must detect whether file capabilities can be assigned, and assign them if so but set setuid-root otherwise. The program in turn must know how to drop partial capabilities, and do so only if setuid-root. This patch introduces v3 of the security.capability xattr. It builds a vfs_ns_cap_data struct by appending a uid_t rootid to struct vfs_cap_data. This is the absolute uid_t (that is, the uid_t in user namespace which mounted the filesystem, usually init_user_ns) of the root id in whose namespaces the file capabilities may take effect. When a task asks to write a v2 security.capability xattr, if it is privileged with respect to the userns which mounted the filesystem, then nothing should change. Otherwise, the kernel will transparently rewrite the xattr as a v3 with the appropriate rootid. This is done during the execution of setxattr() to catch user-space-initiated capability writes. Subsequently, any task executing the file which has the noted kuid as its root uid, or which is in a descendent user_ns of such a user_ns, will run the file with capabilities. Similarly when asking to read file capabilities, a v3 capability will be presented as v2 if it applies to the caller's namespace. If a task writes a v3 security.capability, then it can provide a uid for the xattr so long as the uid is valid in its own user namespace, and it is privileged with CAP_SETFCAP over its namespace. The kernel will translate that rootid to an absolute uid, and write that to disk. After this, a task in the writer's namespace will not be able to use those capabilities (unless rootid was 0), but a task in a namespace where the given uid is root will. Only a single security.capability xattr may exist at a time for a given file. A task may overwrite an existing xattr so long as it is privileged over the inode. Note this is a departure from previous semantics, which required privilege to remove a security.capability xattr. This check can be re-added if deemed useful. This allows a simple setxattr to work, allows tar/untar to work, and allows us to tar in one namespace and untar in another while preserving the capability, without risking leaking privilege into a parent namespace. Example using tar: $ cp /bin/sleep sleepx $ mkdir b1 b2 $ lxc-usernsexec -m b:0:100000:1 -m b:1:$(id -u):1 -- chown 0:0 b1 $ lxc-usernsexec -m b:0:100001:1 -m b:1:$(id -u):1 -- chown 0:0 b2 $ lxc-usernsexec -m b:0:100000:1000 -- tar --xattrs-include=security.capability --xattrs -cf b1/sleepx.tar sleepx $ lxc-usernsexec -m b:0:100001:1000 -- tar --xattrs-include=security.capability --xattrs -C b2 -xf b1/sleepx.tar $ lxc-usernsexec -m b:0:100001:1000 -- getcap b2/sleepx b2/sleepx = cap_sys_admin+ep # /opt/ltp/testcases/bin/getv3xattr b2/sleepx v3 xattr, rootid is 100001 A patch to linux-test-project adding a new set of tests for this functionality is in the nsfscaps branch at github.com/hallyn/ltp Changelog: Nov 02 2016: fix invalid check at refuse_fcap_overwrite() Nov 07 2016: convert rootid from and to fs user_ns (From ebiederm: mar 28 2017) commoncap.c: fix typos - s/v4/v3 get_vfs_caps_from_disk: clarify the fs_ns root access check nsfscaps: change the code split for cap_inode_setxattr() Apr 09 2017: don't return v3 cap for caps owned by current root. return a v2 cap for a true v2 cap in non-init ns Apr 18 2017: . Change the flow of fscap writing to support s_user_ns writing. . Remove refuse_fcap_overwrite(). The value of the previous xattr doesn't matter. Apr 24 2017: . incorporate Eric's incremental diff . move cap_convert_nscap to setxattr and simplify its usage May 8, 2017: . fix leaking dentry refcount in cap_inode_getsecurity Signed-off-by: Serge Hallyn Signed-off-by: Eric W. Biederman

commoncap: Move cap_elevated calculation into bprm_set_creds

2017-08-01T19:03:09Z

Instead of a separate function, open-code the cap_elevated test, which lets us entirely remove bprm->cap_effective (to use the local "effective" variable instead), and more accurately examine euid/egid changes via the existing local "is_setid". The following LTP tests were run to validate the changes: # ./runltp -f syscalls -s cap # ./runltp -f securebits # ./runltp -f cap_bounds # ./runltp -f filecaps All kernel selftests for capabilities and exec continue to pass as well. Signed-off-by: Kees Cook Reviewed-by: James Morris Acked-by: Serge Hallyn Reviewed-by: Andy Lutomirski