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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: #13596
Signed-off-by: Christian Brabandt <cb@256bit.org>
This commit is contained in:
Christian Brabandt
2023-11-30 11:32:18 +01:00
parent b39b240c38
commit abfa13ebe9
4 changed files with 16 additions and 3 deletions
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4
src/ex_cmds.c
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@@ -4650,7 +4650,7 @@ ex_substitute(exarg_T *eap)
* too many calls to alloc()/free()).
*/
new_start_len = needed_len + 50;
if ((new_start = alloc(new_start_len)) == NULL)
if ((new_start = alloc_clear(new_start_len)) == NULL)
goto outofmem;
*new_start = NUL;
new_end = new_start;
@@ -4667,7 +4667,7 @@ ex_substitute(exarg_T *eap)
if (needed_len > (int)new_start_len)
{
new_start_len = needed_len + 50;
if ((p1 = alloc(new_start_len)) == NULL)
if ((p1 = alloc_clear(new_start_len)) == NULL)
{
vim_free(new_start);
goto outofmem;