https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106284
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by David Malcolm <dmalc...@gcc.gnu.org>: https://gcc.gnu.org/g:0a8edfbd37d399d1103d86e134ba0a92f8c873c3 commit r13-1713-g0a8edfbd37d399d1103d86e134ba0a92f8c873c3 Author: David Malcolm <dmalc...@redhat.com> Date: Fri Jul 15 11:28:34 2022 -0400 analyzer: fix taint false positive on optimized range checks [PR106284] PR analyzer/106284 reports a false positive from -Wanalyzer-tainted-array-index seen on the Linux kernel with a version of my patches from: https://gcc.gnu.org/pipermail/gcc-patches/2021-November/584372.html in drivers/usb/class/usblp.c in function âusblp_set_protocolâ handling usblp_ioctl on IOCNR_SET_PROTOCOL, which has: | 1337 | if (protocol < USBLP_FIRST_PROTOCOL || protocol > USBLP_LAST_PROTOCOL) | | ~ | | | | | (15) following âfalseâ branch... |...... | 1341 | if (usblp->intf->num_altsetting > 1) { | | ~~~~~~~~~~~~ | | | | | | | (16) ...to here | | (17) following âtrueâ branch... | 1342 | alts = usblp->protocol[protocol].alt_setting; | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | | | | (18) ...to here | | (19) use of attacker-controlled value âargâ in array lookup without bounds checking where "arg" is "protocol" (albeit from the caller frame, the ioctl callback), and is clearly checked at (15). The root cause is that at -O1 and above fold-const's build_range-check can optimize range checks (c>=low) && (c<=high) into (c-low>=0) && (c-low<=high-low) and thus into a single check: (unsigned)(c - low) <= (unsigned)(high-low). I initially attempted to fix this by detecting such conditions in region_model::on_condition, and calling on_condition for both of the implied conditions. This turned out not to work since the current sm_context framework doesn't support applying two conditions simultaneously: it led to a transition from the old state to has_lb, then a transition from the old state *again* to has_ub, thus leaving the new state as has_ub, rather than the stop state. Instead, this patch fixes things by special-casing it within taint_state_machine::on_condition. gcc/analyzer/ChangeLog: PR analyzer/106284 * sm-taint.cc (taint_state_machine::on_condition): Handle range checks optimized by build_range_check. gcc/testsuite/ChangeLog: PR analyzer/106284 * gcc.dg/analyzer/torture/taint-read-index-2.c: New test. Signed-off-by: David Malcolm <dmalc...@redhat.com>
