If the caller, in this case efivarfs_callback(), only provides sufficent
room for the expanded utf8 and not enough to include the terminating NUL
byte, that NUL byte is skipped. When the caller then interprets it as a
string, it may then read from past its allocated memory:
[ 170.605647] WARNING: kmemcheck: Caught 8-bit read from uninitialized memory (ffff8804079ae786)
[ 170.605677] 436f6e4f757400004c44322d35363062663538612d316530642d346437652d39
[ 170.606037] i i i i i i u u u u u u u u u u u u u u u u u u u u u u u u u u
[ 170.606236] ^
[ 170.606243] RIP: 0010:[<ffffffff813a251f>] [<ffffffff813a251f>] efivar_variable_is_removable+0xaf/0xf0
[ 170.606346] RSP: 0018:ffff880408e73c20 EFLAGS: 00010206
[ 170.606352] RAX: 0000000000000000 RBX: 0000000000000006 RCX: 0000000000000006
[ 170.606359] RDX: 0000000000000000 RSI: 0000000000000074 RDI: ffff880408e73c30
[ 170.606365] RBP: ffff880408e73c80 R08: 0000000000000006 R09: 000000000000008c
[ 170.606371] R10: 0000000000000006 R11: 0000000000000000 R12: ffffffff8166ed20
[ 170.606378] R13: 11d293ca8be4df61 R14: ffffffff81773834 R15: ffff8804079ae780
[ 170.606385] FS: 0000000000000000(0000) GS:ffff88041ca00000(0000) knlGS:0000000000000000
[ 170.606392] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 170.606399] CR2: ffff880409cbe4c0 CR3: 00000004085fd000 CR4: 00000000001406f0
[ 170.606405] [<ffffffff811eb938>] efivarfs_callback+0xf8/0x275
[ 170.606418] [<ffffffff813a3368>] efivar_init+0x248/0x2e0
[ 170.606440] [<ffffffff811eb6b4>] efivarfs_fill_super+0xb4/0xf0
[ 170.606452] [<ffffffff811333e7>] mount_single+0x87/0xb0
[ 170.606463] [<ffffffff811eb5f3>] efivarfs_mount+0x13/0x20
[ 170.606475] [<ffffffff81133480>] mount_fs+0x10/0x90
[ 170.606497] [<ffffffff8114c732>] vfs_kern_mount+0x62/0x100
[ 170.606508] [<ffffffff8114ecb0>] do_mount+0x1e0/0xcd0
[ 170.606519] [<ffffffff8114fa9f>] SyS_mount+0x8f/0xd0
[ 170.606530] [<ffffffff81451d1f>] entry_SYSCALL_64_fastpath+0x17/0x93
[ 170.606542] [<ffffffffffffffff>] 0xffffffffffffffff
Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Cc: Jason Andryuk <jandryuk@xxxxxxxxx>
Cc: Matthew Garrett <mjg59@xxxxxxxxxx>
Cc: Laszlo Ersek <lersek@xxxxxxxxxx>
Cc: Peter Jones <pjones@xxxxxxxxxx>
Cc: linux-efi@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
drivers/firmware/efi/vars.c | 2 +-
lib/ucs2_string.c | 15 ++++++++++-----
2 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 0ac594c0a234..8dd503bac35d 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -166,7 +166,7 @@ validate_ascii_string(efi_char16_t *var_name, int match, u8 *buffer,
struct variable_validate {
efi_guid_t vendor;
- char *name;
+ const char *name;
bool (*validate)(efi_char16_t *var_name, int match, u8 *data,
unsigned long len);
};
diff --git a/lib/ucs2_string.c b/lib/ucs2_string.c
index f0b323abb4c6..fb8d03966656 100644
--- a/lib/ucs2_string.c
+++ b/lib/ucs2_string.c
@@ -85,29 +85,34 @@ ucs2_as_utf8(u8 *dest, const ucs2_char_t *src, unsigned long maxlength)
unsigned long j = 0;
unsigned long limit = ucs2_strnlen(src, maxlength);
- for (i = 0; maxlength && i < limit; i++) {
+ if (maxlength == 0)
+ return 0;
+
+ for (i = 0; i < limit; i++) {
u16 c = src[i];
if (c >= 0x800) {
- if (maxlength < 3)
+ if (maxlength <= 3)
break;
maxlength -= 3;
dest[j++] = 0xe0 | (c & 0xf000) >> 12;
dest[j++] = 0x80 | (c & 0x0fc0) >> 6;
dest[j++] = 0x80 | (c & 0x003f);
} else if (c >= 0x80) {
- if (maxlength < 2)
+ if (maxlength <= 2)
break;
maxlength -= 2;
dest[j++] = 0xc0 | (c & 0x7c0) >> 6;
dest[j++] = 0x80 | (c & 0x03f);
} else {
+ if (maxlength <= 1)
+ break;
maxlength -= 1;
dest[j++] = c & 0x7f;
}
}
- if (maxlength)
- dest[j] = '\0';
+ dest[j] = '\0';
+
return j;
}
EXPORT_SYMBOL(ucs2_as_utf8);
--
2.8.1
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