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From: Michael Tokarev <mjt@tls.msk.ru>
Date: Sun, 19 Jan 2025 12:15:51 +0300
Subject: [PATCH] vvfat: create_long_filename: fix out-of-bounds array access
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=?UTF-8?q?Volker=20R=C3=BCmelin?= <vr_qemu@t-online.de>
Cc: Pierrick Bouvier <pierrick.bouvier@linaro.org>, qemu-block@nongnu.org,
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create_long_filename() intentionally uses direntry_t->name[8+3] array
as a larger array. This works, but makes statid code analysis tools
unhappy. The problem here is that a directory entry holding long file
name is significantly different from regular directory entry, and the
name is split into several parts within the entry, not just in regular
8+3 name field.
Treat the entry as array of bytes instead. This fixes the OOB access
from the compiler/tools PoV, but does not change the resulting code
in any way.
Keep the existing code style.
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
---
block/vvfat.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
This code is really ugly and insanely ineffecient.
But LFN is also ugly.
I think this one is the best for now.
Another patch might optimize the second loop quite a bit,
add comments (since it is really difficult to understand,
especially since lfn is so weird), and fix coding style.
diff --git a/block/vvfat.c b/block/vvfat.c
index bb80dfb177..b53e3b452b 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -403,7 +403,6 @@ static direntry_t *create_long_filename(BDRVVVFATState =
*s, const char *filename)
{
int number_of_entries, i;
glong length;
- direntry_t *entry;
=20
gunichar2 *longname =3D g_utf8_to_utf16(filename, -1, NULL, &length, N=
ULL);
if (!longname) {
@@ -414,24 +413,24 @@ static direntry_t *create_long_filename(BDRVVVFATStat=
e *s, const char *filename)
number_of_entries =3D DIV_ROUND_UP(length * 2, 26);
=20
for(i=3D0;i<number_of_entries;i++) {
- entry=3Darray_get_next(&(s->directory));
+ direntry_t *entry=3Darray_get_next(&(s->directory));
entry->attributes=3D0xf;
entry->reserved[0]=3D0;
entry->begin=3D0;
entry->name[0]=3D(number_of_entries-i)|(i=3D=3D0?0x40:0);
}
for(i=3D0;i<26*number_of_entries;i++) {
+ unsigned char *entry=3Darray_get(&(s->directory),s->directory.next=
-1-(i/26));
int offset=3D(i%26);
if(offset<10) offset=3D1+offset;
else if(offset<22) offset=3D14+offset-10;
else offset=3D28+offset-22;
- entry=3Darray_get(&(s->directory),s->directory.next-1-(i/26));
if (i >=3D 2 * length + 2) {
- entry->name[offset] =3D 0xff;
+ entry[offset] =3D 0xff;
} else if (i % 2 =3D=3D 0) {
- entry->name[offset] =3D longname[i / 2] & 0xff;
+ entry[offset] =3D longname[i / 2] & 0xff;
} else {
- entry->name[offset] =3D longname[i / 2] >> 8;
+ entry[offset] =3D longname[i / 2] >> 8;
}
}
g_free(longname);
--=20
2.39.5