scripts/kallsyms.c: fix potential segfault
PATCH 1/1 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.
--- scripts/kallsyms.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-)
scripts/kallsyms.c +2 -0
@@ -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 ;
Signature · 1 line
1.7.2.3
Quoted 20 lines · Xiaochen Wang
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()inoptimize_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.
Quoted 8 lines
As a result,
expand_symbol(best_table[0]="\0\0", best_table_len[0]=2, buf)inwrite_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 inoptimize_result().
Andexpand_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.
Signature · 3 lines
Paulo Marques - www.grupopie.com "Conservation of angular momentum makes the world go around" - John Clark
Quoted 30 lines · Xiaochen Wang
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()inoptimize_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)inwrite_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 inoptimize_result().
Andexpand_symbol()works well when best_table_len[i] is 0.
Quoted 4 lines
Signed-off-by Xiaochen Wang <[email protected]>--- scripts/kallsyms.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-)
Pushed to kbuild-2.6.git#kbuild, thanks.
Michal