5.4-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Chancellor nathan@kernel.org
commit 1a807e46aa93ebad1dfbed4f82dc3bf779423a6e upstream.
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 Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: Steffen Klassert steffen.klassert@secunet.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/xfrm/xfrm_user.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/net/xfrm/xfrm_user.c +++ b/net/xfrm/xfrm_user.c @@ -1704,6 +1704,9 @@ static int copy_to_user_tmpl(struct xfrm 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];