After a couple recent changes in LLVM, there is a warning (or error with CONFIG_WERROR=y or W=e) from the compile time fortify source routines, specifically the memset() in copy_to_user_tmpl().
In file included from net/xfrm/xfrm_user.c:14: ... include/linux/fortify-string.h:438:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning] 438 | __write_overflow_field(p_size_field, size); | ^ 1 error generated.
While ->xfrm_nr has been validated against XFRM_MAX_DEPTH when its value is first assigned in copy_templates() by calling validate_tmpl() first (so there should not be any issue in practice), LLVM/clang cannot really deduce that across the boundaries of these functions. Without that knowledge, it cannot assume that the loop stops before i is greater than XFRM_MAX_DEPTH, which would indeed result a stack buffer overflow in the memset().
To make the bounds of ->xfrm_nr clear to the compiler and add additional defense in case copy_to_user_tmpl() is ever used in a path where ->xfrm_nr has not been properly validated against XFRM_MAX_DEPTH first, add an explicit bound check and early return, which clears up the warning.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1985 Signed-off-by: Nathan Chancellor nathan@kernel.org --- net/xfrm/xfrm_user.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c index f037be190bae..912c1189ba41 100644 --- a/net/xfrm/xfrm_user.c +++ b/net/xfrm/xfrm_user.c @@ -2017,6 +2017,9 @@ static int copy_to_user_tmpl(struct xfrm_policy *xp, struct sk_buff *skb) if (xp->xfrm_nr == 0) return 0;
+ if (xp->xfrm_nr > XFRM_MAX_DEPTH) + return -ENOBUFS; + for (i = 0; i < xp->xfrm_nr; i++) { struct xfrm_user_tmpl *up = &vec[i]; struct xfrm_tmpl *kp = &xp->xfrm_vec[i];
--- base-commit: 14dec56fdd4c70a0ebe40077368e367421ea6fef change-id: 20240221-xfrm-avoid-clang-fortify-warning-copy_to_user_tmpl-40cb10b003e3
Best regards,
On Wed, Feb 21, 2024 at 02:46:21PM -0700, Nathan Chancellor wrote:
After a couple recent changes in LLVM, there is a warning (or error with CONFIG_WERROR=y or W=e) from the compile time fortify source routines, specifically the memset() in copy_to_user_tmpl().
In file included from net/xfrm/xfrm_user.c:14: ... include/linux/fortify-string.h:438:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning] 438 | __write_overflow_field(p_size_field, size); | ^ 1 error generated.
While ->xfrm_nr has been validated against XFRM_MAX_DEPTH when its value is first assigned in copy_templates() by calling validate_tmpl() first (so there should not be any issue in practice), LLVM/clang cannot really deduce that across the boundaries of these functions. Without that knowledge, it cannot assume that the loop stops before i is greater than XFRM_MAX_DEPTH, which would indeed result a stack buffer overflow in the memset().
To make the bounds of ->xfrm_nr clear to the compiler and add additional defense in case copy_to_user_tmpl() is ever used in a path where ->xfrm_nr has not been properly validated against XFRM_MAX_DEPTH first, add an explicit bound check and early return, which clears up the warning.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1985 Signed-off-by: Nathan Chancellor nathan@kernel.org
This seems reasonable to me. Thanks for chasing all this down!
Reviewed-by: Kees Cook keescook@chromium.org
-Kees
net/xfrm/xfrm_user.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c index f037be190bae..912c1189ba41 100644 --- a/net/xfrm/xfrm_user.c +++ b/net/xfrm/xfrm_user.c @@ -2017,6 +2017,9 @@ static int copy_to_user_tmpl(struct xfrm_policy *xp, struct sk_buff *skb) if (xp->xfrm_nr == 0) return 0;
- if (xp->xfrm_nr > XFRM_MAX_DEPTH)
return -ENOBUFS;- for (i = 0; i < xp->xfrm_nr; i++) { struct xfrm_user_tmpl *up = &vec[i]; struct xfrm_tmpl *kp = &xp->xfrm_vec[i];
base-commit: 14dec56fdd4c70a0ebe40077368e367421ea6fef change-id: 20240221-xfrm-avoid-clang-fortify-warning-copy_to_user_tmpl-40cb10b003e3
Best regards,
Nathan Chancellor nathan@kernel.org
On Wed, Feb 21, 2024 at 02:46:21PM -0700, Nathan Chancellor wrote:
After a couple recent changes in LLVM, there is a warning (or error with CONFIG_WERROR=y or W=e) from the compile time fortify source routines, specifically the memset() in copy_to_user_tmpl().
In file included from net/xfrm/xfrm_user.c:14: ... include/linux/fortify-string.h:438:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning] 438 | __write_overflow_field(p_size_field, size); | ^ 1 error generated.
While ->xfrm_nr has been validated against XFRM_MAX_DEPTH when its value is first assigned in copy_templates() by calling validate_tmpl() first (so there should not be any issue in practice), LLVM/clang cannot really deduce that across the boundaries of these functions. Without that knowledge, it cannot assume that the loop stops before i is greater than XFRM_MAX_DEPTH, which would indeed result a stack buffer overflow in the memset().
To make the bounds of ->xfrm_nr clear to the compiler and add additional defense in case copy_to_user_tmpl() is ever used in a path where ->xfrm_nr has not been properly validated against XFRM_MAX_DEPTH first, add an explicit bound check and early return, which clears up the warning.
Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1985 Signed-off-by: Nathan Chancellor nathan@kernel.org
Applied to the ipsec tree, thanks a lot!
linux-stable-mirror@lists.linaro.org
-
Kees Cook -
Nathan Chancellor -
Steffen Klassert