From 88674f03955160f591067ce83dc3b7819a39e885 Mon Sep 17 00:00:00 2001 From: Petr Vandrovec Date: Wed, 15 Jan 2020 12:44:52 -0800 Subject: [PATCH] gobuffer: Do not crash on object without any public symbols pahole -J .tmp_linux.btf during Linux build process always crashes on my system. Problem is that when gobuffer is initialized via gobuffer__init(), it is in state where 'index' (AKA its size) is set to 1, but 'entries' is NULL. State corrects itself if 'gobuffer__add()' is invoked, as that will allocate buffer (even if added len == 0). But if __add() is never invoked because only anonymous symbols are present, one ends up with gobuffer that crashes gobuffer__copy. Instead of allocating single-byte buffer always I opted for checking if gobuffer entries is NULL before use in copy and compress - gobuffer__init() would need prototype change to report malloc failures, and it seems unnecessary to allocate memory always - even if file does not have any symbols after all. (gdb) bt #0 __memmove_sse2_unaligned_erms () at ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:287 #1 0x00007f2f2c1ec2ee in btf_elf__encode (btfe=0x5654e31e2e30, flags=flags@entry=0 '\000') at libbtf.c:750 #2 0x00007f2f2c1e9af0 in btf_encoder__encode () at btf_encoder.c:164 #3 0x00005654e2407599 in main (argc=3, argv=0x7ffcd8783f18) at pahole.c:1344 (gdb) frame 1 #1 0x00007f2f2c1ec2ee in btf_elf__encode (btfe=0x5654e31e2e30, flags=flags@entry=0 '\000') at libbtf.c:750 750 gobuffer__copy(btfe->strings, btf_elf__nohdr_data(btfe) + hdr->str_off); (gdb) print btfe->strings $1 = (struct gobuffer *) 0x5654e31db2c8 (gdb) print *btfe->strings $2 = {entries = 0x0, nr_entries = 0, index = 1, allocated_size = 0} (gdb) print btfe->types $3 = {entries = 0x5654e31e2ef0 "", nr_entries = 1, index = 16, allocated_size = 8192} (gdb) x /16bx btfe->types.entries 0x5654e31e2ef0: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x5654e31e2ef8: 0x04 0x00 0x00 0x00 0x20 0x00 0x00 0x00 Signed-off-by: Petr Vandrovec Signed-off-by: Arnaldo Carvalho de Melo --- gobuffer.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/gobuffer.c b/gobuffer.c index f8d2066..1ea823b 100644 --- a/gobuffer.c +++ b/gobuffer.c @@ -91,7 +91,12 @@ int gobuffer__add(struct gobuffer *gb, const void *s, unsigned int len) void gobuffer__copy(const struct gobuffer *gb, void *dest) { - memcpy(dest, gb->entries, gobuffer__size(gb)); + if (gb->entries) { + memcpy(dest, gb->entries, gobuffer__size(gb)); + } else { + /* gobuffer__size will be 0 or 1. */ + memcpy(dest, "", gobuffer__size(gb)); + } } const void *gobuffer__compress(struct gobuffer *gb, unsigned int *size) @@ -101,7 +106,7 @@ const void *gobuffer__compress(struct gobuffer *gb, unsigned int *size) .zfree = Z_NULL, .opaque = Z_NULL, .avail_in = gobuffer__size(gb), - .next_in = (Bytef *)gobuffer__entries(gb), + .next_in = (Bytef *)(gobuffer__entries(gb) ? : ""), }; void *bf = NULL; unsigned int bf_size = 0;