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vim-patch:9.0.2143: [security]: buffer-overflow in ex_substitute

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Problem:  [security]: buffer-overflow in ex_substitute
Solution: clear memory after allocating

When allocating the new_start pointer in ex_substitute() the memory
pointer points to some garbage that the following for loop in
ex_cmds.c:4743 confuses and causes it to accessing the new_start pointer
beyond it's size, leading to a buffer-overlow.

So fix this by using alloc_clear() instead of alloc(), which will
clear the memory by NUL and therefore cause the loop to terminate
correctly.

Reported by @henices, thanks!

closes: vim/vim#13596

abfa13ebe9

Co-authored-by: Christian Brabandt <cb@256bit.org>
This commit is contained in:
zeertzjq 2023-12-02 10:17:43 +08:00
parent 9cc346119b
commit 9d7544ac4c
3 changed files with 16 additions and 2 deletions
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5
src/nvim/ex_cmds.c
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@ -3144,7 +3144,7 @@ static char *sub_grow_buf(char **new_start, int *new_start_len, int needed_len)
// substitution into (and some extra space to avoid
// too many calls to xmalloc()/free()).
*new_start_len = needed_len + 50;
*new_start = xmalloc((size_t)(*new_start_len));
*new_start = xcalloc(1, (size_t)(*new_start_len));
**new_start = NUL;
new_end = *new_start;
} else {
@ -3154,8 +3154,11 @@ static char *sub_grow_buf(char **new_start, int *new_start_len, int needed_len)
size_t len = strlen(*new_start);
needed_len += (int)len;
if (needed_len > *new_start_len) {
size_t prev_new_start_len = (size_t)(*new_start_len);
*new_start_len = needed_len + 50;
size_t added_len = (size_t)(*new_start_len) - prev_new_start_len;
*new_start = xrealloc(*new_start, (size_t)(*new_start_len));
memset(*new_start + prev_new_start_len, 0, added_len);
}
new_end = *new_start + len;
}

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test/old/testdir/crash/poc_ex_substitute Normal file
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13
test/old/testdir/test_crash.vim
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@ -117,7 +117,7 @@ func Test_crash1_2()
" The following used to crash Vim
let opts = #{cmd: 'sh'}
let vim = GetVimProg()
let result = 'X_crash1_1_result.txt'
let result = 'X_crash1_2_result.txt'
let buf = RunVimInTerminal('sh', opts)
@ -149,6 +149,17 @@ func Test_crash1_2()
\ ' ; echo "crash 4: [OK]" >> '.. result .. "\<cr>")
call TermWait(buf, 150)
let file = 'crash/poc_ex_substitute'
let cmn_args = "%s -u NONE -i NONE -n -e -s -S %s -c ':qa!'"
let args = printf(cmn_args, vim, file)
" just make sure it runs, we don't care about the resulting echo
call term_sendkeys(buf, args .. "\<cr>")
" There is no output generated in Github CI for the asan clang build.
" so just skip generating the ouput.
" call term_sendkeys(buf, args ..
" \ ' && echo "crash 5: [OK]" >> '.. result .. "\<cr>")
call TermWait(buf, 150)
" clean up
exe buf .. "bw!"