Calling uname() with the UNAME26 personality set allows a leak of kernel stack contents. This fixes it by defensively calculating the length of copy_to_user() call, making the len argument unsigned, and initializing the stack buffer to zero (now technically unneeded, but hey, overkill).
CVE-2012-0957 Reported-by: PaX Team <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Andi Kleen <[email protected]> Cc: PaX Team <[email protected]> Cc: Brad Spengler <[email protected]> Cc: [email protected] Signed-off-by: Kees Cook <[email protected]> --- v4: - switch to clamp_t, thanks to Fengguang Wu. v3: - use scnprintf, suggested by Andrew Morton. v2: - corrected credit to PaX Team. - moved stack clearing into if case to avoid penalty to common case. --- kernel/sys.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/sys.c b/kernel/sys.c index c5cb5b9..e6e0ece 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1265,15 +1265,16 @@ DECLARE_RWSEM(uts_sem); * Work around broken programs that cannot handle "Linux 3.0". * Instead we map 3.x to 2.6.40+x, so e.g. 3.0 would be 2.6.40 */ -static int override_release(char __user *release, int len) +static int override_release(char __user *release, size_t len) { int ret = 0; - char buf[65]; if (current->personality & UNAME26) { - char *rest = UTS_RELEASE; + const char *rest = UTS_RELEASE; + char buf[65] = { 0 }; int ndots = 0; unsigned v; + size_t copy; while (*rest) { if (*rest == '.' && ++ndots >= 3) @@ -1283,8 +1284,9 @@ static int override_release(char __user *release, int len) rest++; } v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40; - snprintf(buf, len, "2.6.%u%s", v, rest); - ret = copy_to_user(release, buf, len); + copy = clamp_t(size_t, len, 1, sizeof(buf)); + copy = scnprintf(buf, copy, "2.6.%u%s", v, rest); + ret = copy_to_user(release, buf, copy + 1); } return ret; } -- 1.7.9.5 -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
