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pahole: Avoid segfault when parsing bogus file

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When trying to use BTF encoding for an apparently problematic kernel
file, pahole segfaults. As can be seen below [1], the problem is that we
are trying to dereference a NULL decoder.

Fix this by checking the return value of dwfl_getmodules which [2] will
return -1 on errors or an offset if one of the modules did not return
DWARF_CB_OK. (In this specific case, it was __cus__load_debug_types that
returned DWARF_CB_ABORT.)

[1]:

  $ gdb -q --args ./pahole -J vmlinux-5.3.18-24.102-default.debug
  Reading symbols from ./pahole...
  (gdb) r
  Starting program: /tmp/pahole/build/pahole -J vmlinux-5.3.18-24.102-default.debug
  [Thread debugging using libthread_db enabled]
  Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

  Program received signal SIGSEGV, Segmentation fault.
  0x00007ffff7f4000e in gobuffer__size (gb=0x18) at /tmp/pahole/gobuffer.h:39
  39              return gb->index;
  (gdb) bt
  (gdb) frame 1
  1042            if (gobuffer__size(&encoder->percpu_secinfo) != 0)
  (gdb) list
  1037
  1038    int btf_encoder__encode(struct btf_encoder *encoder)
  1039    {
  1040            int err;
  1041
  1042            if (gobuffer__size(&encoder->percpu_secinfo) != 0)
  1043                    btf_encoder__add_datasec(encoder, PERCPU_SECTION);
  1044
  1045            /* Empty file, nothing to do, so... done! */
  1046            if (btf__get_nr_types(encoder->btf) == 0)
  (gdb) print encoder
  $1 = (struct btf_encoder *) 0x0

[2] https://sourceware.org/git/?p=elfutils.git;a=blob;f=libdwfl/libdwfl.h;h=f98f1d525d94bc7bcfc7c816890de5907ee4bd6d;hb=HEAD#l200

Signed-off-by: Kornilios Kourtis <kornilios@isovalent.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Link: http://lore.kernel.org/lkml/20220316132338.3226871-1-kkourt@kkourt.io
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Kornilios Kourtis 2022-03-16 14:23:38 +01:00 committed by Arnaldo Carvalho de Melo
parent 65d7273668
commit f952a6f69f
1 changed files with 3 additions and 1 deletions
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4
dwarf_loader.c
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@ -3268,7 +3268,9 @@ static int cus__process_file(struct cus *cus, struct conf_load *conf, int fd,
};
/* Process the one or more modules gleaned from this file. */
dwfl_getmodules(dwfl, cus__process_dwflmod, &parms, 0);
int err = dwfl_getmodules(dwfl, cus__process_dwflmod, &parms, 0);
if (err)
return -1;
// We can't call dwfl_end(dwfl) here, as we keep pointers to strings
// allocated by libdw that will be freed at dwfl_end(), so leave this for