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scripts/kallsyms.c: fix potential segfault

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.

Signed-off-by: Xiaochen Wang <wangxiaochen0@gmail.com>
Acked-by: Paulo Marques <pmarques@grupopie.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
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commit e0a04b11e4059cab033469617c2a3ce2d8cab416 1 parent 153f011
@chobits chobits authored michal42 committed
Showing with 2 additions and 0 deletions.
  1. +2 −0  scripts/kallsyms.c
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2  scripts/kallsyms.c
@@ -500,6 +500,8 @@ static void optimize_result(void)
/* find the token with the breates profit value */
best = find_best_token();
+ if (token_profit[best] == 0)
+ break;
/* place it in the "best" table */
best_table_len[i] = 2;
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