From 4e5e705c5f3bf0cc704c0cf9d7c5ffff6d6b8846 Mon Sep 17 00:00:00 2001 From: Salvatore Bonaccorso Date: Wed, 15 Feb 2017 11:44:15 +0100 Subject: [PATCH] selinux: fix off-by-one in setprocattr (CVE-2017-2618) --- debian/changelog | 1 + ...elinux-fix-off-by-one-in-setprocattr.patch | 65 +++++++++++++++++++ debian/patches/series | 1 + 3 files changed, 67 insertions(+) create mode 100644 debian/patches/bugfix/all/selinux-fix-off-by-one-in-setprocattr.patch diff --git a/debian/changelog b/debian/changelog index 40dd46163..4a066b0f2 100644 --- a/debian/changelog +++ b/debian/changelog @@ -196,6 +196,7 @@ linux (4.9.9-1) UNRELEASED; urgency=medium [ Salvatore Bonaccorso ] * IB/rxe: Fix mem_check_range integer overflow (CVE-2016-8636) + * selinux: fix off-by-one in setprocattr (CVE-2017-2618) -- Ben Hutchings Fri, 27 Jan 2017 18:14:31 +0000 diff --git a/debian/patches/bugfix/all/selinux-fix-off-by-one-in-setprocattr.patch b/debian/patches/bugfix/all/selinux-fix-off-by-one-in-setprocattr.patch new file mode 100644 index 000000000..fcb9491e3 --- /dev/null +++ b/debian/patches/bugfix/all/selinux-fix-off-by-one-in-setprocattr.patch @@ -0,0 +1,65 @@ +From: Stephen Smalley +Date: Tue, 31 Jan 2017 11:54:04 -0500 +Subject: selinux: fix off-by-one in setprocattr +Origin: https://git.kernel.org/linus/0c461cb727d146c9ef2d3e86214f498b78b7d125 + +SELinux tries to support setting/clearing of /proc/pid/attr attributes +from the shell by ignoring terminating newlines and treating an +attribute value that begins with a NUL or newline as an attempt to +clear the attribute. However, the test for clearing attributes has +always been wrong; it has an off-by-one error, and this could further +lead to reading past the end of the allocated buffer since commit +bb646cdb12e75d82258c2f2e7746d5952d3e321a ("proc_pid_attr_write(): +switch to memdup_user()"). Fix the off-by-one error. + +Even with this fix, setting and clearing /proc/pid/attr attributes +from the shell is not straightforward since the interface does not +support multiple write() calls (so shells that write the value and +newline separately will set and then immediately clear the attribute, +requiring use of echo -n to set the attribute), whereas trying to use +echo -n "" to clear the attribute causes the shell to skip the +write() call altogether since POSIX says that a zero-length write +causes no side effects. Thus, one must use echo -n to set and echo +without -n to clear, as in the following example: +$ echo -n unconfined_u:object_r:user_home_t:s0 > /proc/$$/attr/fscreate +$ cat /proc/$$/attr/fscreate +unconfined_u:object_r:user_home_t:s0 +$ echo "" > /proc/$$/attr/fscreate +$ cat /proc/$$/attr/fscreate + +Note the use of /proc/$$ rather than /proc/self, as otherwise +the cat command will read its own attribute value, not that of the shell. + +There are no users of this facility to my knowledge; possibly we +should just get rid of it. + +UPDATE: Upon further investigation it appears that a local process +with the process:setfscreate permission can cause a kernel panic as a +result of this bug. This patch fixes CVE-2017-2618. + +Signed-off-by: Stephen Smalley +[PM: added the update about CVE-2017-2618 to the commit description] +Cc: stable@vger.kernel.org # 3.5: d6ea83ec6864e +Signed-off-by: Paul Moore + +Signed-off-by: James Morris +--- + security/selinux/hooks.c | 2 +- + 1 file changed, 1 insertion(+), 1 deletion(-) + +diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c +index c7c6619..d98550a 100644 +--- a/security/selinux/hooks.c ++++ b/security/selinux/hooks.c +@@ -5887,7 +5887,7 @@ static int selinux_setprocattr(struct task_struct *p, + return error; + + /* Obtain a SID for the context, if one was specified. */ +- if (size && str[1] && str[1] != '\n') { ++ if (size && str[0] && str[0] != '\n') { + if (str[size-1] == '\n') { + str[size-1] = 0; + size--; +-- +2.1.4 + diff --git a/debian/patches/series b/debian/patches/series index a2a8e335d..dfab2f599 100644 --- a/debian/patches/series +++ b/debian/patches/series @@ -105,6 +105,7 @@ features/all/securelevel/arm64-add-kernel-config-option-to-set-securelevel-wh.pa # Security fixes debian/i386-686-pae-pci-set-pci-nobios-by-default.patch bugfix/all/IB-rxe-Fix-mem_check_range-integer-overflow.patch +bugfix/all/selinux-fix-off-by-one-in-setprocattr.patch # Fix exported symbol versions bugfix/ia64/revert-ia64-move-exports-to-definitions.patch