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patch 9.1.1688: potential buffer overrun in bufwrite.c

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Problem:  potential buffer overrun in bufwrite.c
Solution: Use a temporary variable (John Marriott)

In my Windows 11 Pro 64-bit build MAXPATHL is 1024 and IOSIZE is 1025.
In my Archlinux Linux 64-bit build MAXPATHL is 4096 and IOSIZE is 1025.

In funuction buf_write():
There is a check (line 713) that makes sure the length of fname is less
than MAXPATHL. There is a call to STRCPY() (line 1208) which copies the
string at fname into IObuff (which has size IOSIZE). For Unix builds
fname is set to sfname which may or may not be shorter. However, if
sfname is NULL sfname is set to fname.

Therefore, in builds where MAXPATHL > IOSIZE (eg in my linux build), it
is theoretically possible for the STRCPY() call to exceed the bounds of
IObuff.

This PR addresses this by copying fname into a local variable that has
the same maximum size as fname.

In addition:
Given that the filename is unconditionally overwritten in the for loop,
only copy the directory portion of fname. Move variable i closer to
where it is used.

closes: #18095

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>
This commit is contained in:
John Marriott
2025-08-26 17:32:18 +02:00
committed by Christian Brabandt
parent 2b55474f0a
commit a19b019b87
2 changed files with 16 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
src/bufwrite.c
View File

@@ -1173,8 +1173,6 @@ buf_write(
#if defined(UNIX) || defined(MSWIN)
else if ((bkc & BKC_AUTO)) // "auto"
{
int i;
# ifdef UNIX
// Don't rename the file when:
// - it's a hard link
@@ -1201,18 +1199,24 @@ buf_write(
# endif
# endif
{
size_t dirlen;
char_u tmp_fname[MAXPATHL];
int i;
// Check if we can create a file and set the owner/group to
// the ones from the original file.
// First find a file name that doesn't exist yet (use some
// arbitrary numbers).
STRCPY(IObuff, fname);
dirlen = (size_t)(gettail(fname) - fname);
vim_strncpy(tmp_fname, fname, dirlen);
fd = -1;
for (i = 4913; ; i += 123)
{
sprintf((char *)gettail(IObuff), "%d", i);
if (mch_lstat((char *)IObuff, &st) < 0)
vim_snprintf((char *)tmp_fname + dirlen,
sizeof(tmp_fname) - dirlen, "%d", i);
if (mch_lstat((char *)tmp_fname, &st) < 0)
{
fd = mch_open((char *)IObuff,
fd = mch_open((char *)tmp_fname,
O_CREAT|O_WRONLY|O_EXCL|O_NOFOLLOW, perm);
if (fd < 0 && errno == EEXIST)
// If the same file name is created by another
@@ -1230,7 +1234,7 @@ buf_write(
# ifdef HAVE_FCHOWN
vim_ignored = fchown(fd, st_old.st_uid, st_old.st_gid);
# endif
if (mch_stat((char *)IObuff, &st) < 0
if (mch_stat((char *)tmp_fname, &st) < 0
|| st.st_uid != st_old.st_uid
|| st.st_gid != st_old.st_gid
|| (long)st.st_mode != perm)
@@ -1239,7 +1243,7 @@ buf_write(
// Close the file before removing it, on MS-Windows we
// can't delete an open file.
close(fd);
mch_remove(IObuff);
mch_remove(tmp_fname);
# ifdef MSWIN
// MS-Windows may trigger a virus scanner to open the
// file, we can't delete it then. Keep trying for half a
@@ -1249,10 +1253,10 @@ buf_write(
for (try = 0; try < 10; ++try)
{
if (mch_lstat((char *)IObuff, &st) < 0)
if (mch_lstat((char *)tmp_fname, &st) < 0)
break;
ui_delay(50L, TRUE); // wait 50 msec
mch_remove(IObuff);
mch_remove(tmp_fname);
}
}
# endif

2
src/version.c
View File

@@ -724,6 +724,8 @@ static char *(features[]) =
static int included_patches[] =
{ /* Add new patch number below this line */
/**/
1688,
/**/
1687,
/**/