Messages in this thread | | | Date | Tue, 03 May 2011 12:56:00 +0100 | From | Paulo Marques <> | Subject | Re: [PATCH] scripts/kallsyms.c: fix potential segfault |
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Xiaochen Wang wrote: > Description: > This bug hardly appears during real kernel compiling, > because the vmlinux symbols table is huge. > > But we can still catch it under strict condition , as follows. > $ echo "c101b97b T do_fork" | ./scripts/kallsyms --all-symbols > #include <asm/types.h> > ...... > ...... > .globl kallsyms_token_table > ALGN > kallsyms_token_table: > Segmentation fault (core dumped) > $ > > If symbols table is small, all entries in token_profit[0x10000] may > decrease to 0 after several calls of compress_symbols() in optimize_result(). > In that case, find_best_token() always return 0 and > best_table[i] is set to "\0\0" and best_table_len[i] is set to 2. > > As a result, expand_symbol(best_table[0]="\0\0", best_table_len[0]=2, buf) > in write_src() will run in infinite recursion until stack overflows, > causing segfault. > > This patch checks the find_best_token() return value. If all entries in > token_profit[0x10000] become 0 according to return value, it breaks the loop > in optimize_result(). > And expand_symbol() works well when best_table_len[i] is 0.
For this to happen on a real kernel, the list of symbols needs to have less than 256 single characters + two letter sequences, which is highly unlikely. From a quick test, a symbol table of a mere 30 symbols was able to overcome those constraints.
Having said that, the fix is very small, it is not on a hot-path and it is the right thing to do from a correctness stand point, so you have my ack.
Acked-by: Paulo Marques <pmarques@grupopie.com>
-- Paulo Marques - www.grupopie.com
"Conservation of angular momentum makes the world go around" - John Clark
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