linux-kernel - [PATCH v2] Change OPT_STR max to be 1 less than the size of choices array

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Message-ID: <20241106193443.307896-2-pZ010001011111@proton.me>
Date: Wed, 06 Nov 2024 19:46:30 +0000
From: Piotr Zalewski <pZ010001011111@...ton.me>
To: kent.overstreet@...ux.dev, linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: skhan@...uxfoundation.org, Piotr Zalewski <pZ010001011111@...ton.me>, syzbot+bee87a0c3291c06aa8c6@...kaller.appspotmail.com
Subject: [PATCH v2] Change OPT_STR max to be 1 less than the size of choices array

Change OPT_STR max value to be 1 less than the "ARRAY_SIZE" of "_choices"
array. As a result, remove -1 from (opt->max-1) in bch2_opt_to_text.

The "_choices" array is a null-terminated array, so computing the maximum
using "ARRAY_SIZE" without subtracting 1 yields an incorrect result. Since
bch2_opt_validate don't subtract 1, as bch2_opt_to_text does, values
bigger than the actual maximum would pass through option validation.

Reported-by: syzbot+bee87a0c3291c06aa8c6@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bee87a0c3291c06aa8c6
Fixes: 63c4b2545382 ("bcachefs: Better superblock opt validation")
Suggested-by: Kent Overstreet <kent.overstreet@...ux.dev>
Signed-off-by: Piotr Zalewski <pZ010001011111@...ton.me>
---

Notes:
    Changes in v2:
        - Instead of subtracting 1 in bch2_opt_validate as in
          bch2_opt_to_text add -1 in OPT_STR macro definition
          and remove subtraction in bch2_opt_to_text.

    link to v1: https://lore.kernel.org/linux-bcachefs/20241031231823.688918-2-pZ010001011111@proton.me/

 fs/bcachefs/opts.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/opts.c b/fs/bcachefs/opts.c
index 83f55cf99d46..49c59aec6954 100644
--- a/fs/bcachefs/opts.c
+++ b/fs/bcachefs/opts.c
@@ -227,7 +227,7 @@ const struct bch_option bch2_opt_table[] = {
 #define OPT_UINT(_min, _max)	.type = BCH_OPT_UINT,			\
 				.min = _min, .max = _max
 #define OPT_STR(_choices)	.type = BCH_OPT_STR,			\
-				.min = 0, .max = ARRAY_SIZE(_choices),	\
+				.min = 0, .max = ARRAY_SIZE(_choices) - 1, \
 				.choices = _choices
 #define OPT_STR_NOLIMIT(_choices)	.type = BCH_OPT_STR,		\
 				.min = 0, .max = U64_MAX,		\
@@ -429,7 +429,7 @@ void bch2_opt_to_text(struct printbuf *out,
 			prt_printf(out, "%lli", v);
 		break;
 	case BCH_OPT_STR:
-		if (v < opt->min || v >= opt->max - 1)
+		if (v < opt->min || v >= opt->max)
 			prt_printf(out, "(invalid option %lli)", v);
 		else if (flags & OPT_SHOW_FULL_LIST)
 			prt_string_option(out, opt->choices, v);
-- 
2.47.0