https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94527
David Malcolm <dmalcolm at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |dmalcolm at gcc dot gnu.org
--- Comment #9 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
I hadn't seen this bug, but I've just posted:
"[PATCH] RFC: add "deallocated_by" attribute for use by analyzer"
https://gcc.gnu.org/pipermail/gcc-patches/2020-October/555544.html
which does some of the things requested in this RFE, but purely within
-fanalyzer. -fanalyzer is read-only w.r.t. GCC's internal representation, i.e.
it doesn't affect optimizations such as DSE. Though I suppose the same
attribute could also be handled by optimization passes.
That patch has some big limitations, as I noted. I attempted to use this to
mark up:
extern struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags);
extern void usb_free_urb(struct urb *urb);
as an acquire/release pair via:
#define __deallocated_by(f) __attribute__((deallocated_by(f)));
extern struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags)
__deallocated_by(usb_free_urb);
in order to detect CVE-2019-19078, a leak of struct urb in an error-handling
path in linux <= 5.3.11 in drivers/net/wireless/ath/ath10k/usb.c, but I ran
into issues where, without LTO, the analyzer knows nothing about calls to:
usb_fill_bulk_urb
usb_anchor_urb
usb_unanchor_urb
that occur along that path, and so it conservatively assumes it doesn't leak.
(Caveat: I know nothing about those calls either; I'm a user-space developer
with little knowledge of linux internals). I can get -fanalyzer to emit a leak
warning on that code path with that patch if I hack out those calls.
[To set expectations: I should mention that my initial implementation of
-fanalyzer in gcc 10 had some major design flaws that mean it couldn't scale;
I've fixed those flaws for gcc 11, and am working hard on scaling it up to be
usable on real-world C when gcc 11 ships, but I don't feel it's there yet. In
particular, I don't expect the current version in git to be usable with LTO
other than on toy examples without some more fixes. The -fanalyzer option has
found some bugs, including at least one CVE, but I don't recommend it yet other
than to adventurous early adopters. As I said, I hope to have it in much
better shape when GCC 11 actually ships in about 6 months time]
