Messages in this thread Patch in this message | | | From | Arnaldo Carvalho de Melo <> | Date | Mon, 9 Mar 2020 09:48:56 -0300 | Subject | Re: [PATCH] Fix off by one in tools/perf strncpy size argument |
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Em Mon, Mar 09, 2020 at 09:39:40AM -0300, Arnaldo Carvalho de Melo escreveu: > Em Mon, Mar 09, 2020 at 11:48:53AM +0100, Dominik 'disconnect3d' Czarnota escreveu: > > From: disconnect3d <dominik.b.czarnota@gmail.com> > > > > This patch fixes an off-by-one error in strncpy size argument in > > tools/perf/util/map.c. The issue is that in: > > > > strncmp(filename, "/system/lib/", 11) > > > > the passed string literal: "/system/lib/" has 12 bytes (without the NULL > > byte) and the passed size argument is 11. As a result, the logic won't > > match the ending "/" byte and will pass filepaths that are stored in > > other directories e.g. "/system/libmalicious/bin" or just > > "/system/libmalicious". > > > > This functionality seems to be present only on Android. I assume the > > /system/ directory is only writable by the root user, so I don't > > think this bug has much (or any) security impact. > > > > Signed-off-by: disconnect3d <dominik.b.czarnota@gmail.com> > > --- > > > > Notes: > > I can't test this patch, so if someone can, please, do so. > > > > The bug could also be fixed by changing the size argument to `sizeof("string literal")-1` but I am not proposing this change as that would have to be changed in other places. > > So, there are parts of this tools/perf/util/map.c that uses the idiom > you mention, for instance: > > static inline int is_anon_memory(const char *filename, u32 flags) > { > return flags & MAP_HUGETLB || > !strcmp(filename, "//anon") || > !strncmp(filename, "/dev/zero", sizeof("/dev/zero") - 1) || > !strncmp(filename, "/anon_hugepage", sizeof("/anon_hugepage") - 1); > } > > So I think we should make all cases use this idim to avoid these > problems. > > So I'll add your patch, then another, on top, that fixes the other > off-by-one errors introduced by the android specific code in this patch:
This is the only such off-by-one in that file, and I remembered we have strstarts(), that we adopted from the kernel sources, so I think its a better fit, no?
[acme@five linux]$ find . -name "*.c" | grep -v tools/ | xargs grep -w strstarts | wc -l 55 [acme@five linux]$ find tools/ -name "*.c" | xargs grep -w strstarts | wc -l 40 [acme@five linux]$ > Fixes: eca818369996 ("perf tools: Add automatic remapping of Android libraries") > > Put this in perf/urgent and then in perf/core move to the more robust > idiom, > > Thanks, > > - Arnaldo > > > There are also more cases like this in kernel sources which I am going to report soon. > > > > Also please note that other path comparisons in this file lack the "/" at the end and it seems they may imply similar issue. I haven't analysed the code deeply to see if that is a real issue. > > > > This bug has been found by running a massive grep-like search using Google's BigQuery on GitHub repositories data. I am also going to work on a CodeQL/Semmle query to be able to find more sophisticated cases like this that can't be found via grepping. > > > > tools/perf/util/map.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c > > index a08ca276098e..addd7edb0486 100644 > > --- a/tools/perf/util/map.c > > +++ b/tools/perf/util/map.c > > @@ -89,7 +89,7 @@ static inline bool replace_android_lib(const char *filename, char *newfilename) > > return true; > > } > > > > - if (!strncmp(filename, "/system/lib/", 11)) { > > + if (!strncmp(filename, "/system/lib/", 12)) { > > char *ndk, *app; > > const char *arch; > > size_t ndk_length; > > -- > > 2.25.1 > > > > -- > > - Arnaldo
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- Arnaldo
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