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SubjectRe: INFO: rcu detected stall in bitmap_parselist
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Yury, are you OK with this patch?


From 7f21827cdfe9780b4949b22bcd19efa721b463d2 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Wed, 4 Apr 2018 21:12:10 +0900
Subject: [PATCH] lib/bitmap: Rewrite __bitmap_parselist().

syzbot is catching stalls at __bitmap_parselist() [1]. The trigger is

unsigned long v = 0;
bitmap_parselist("7:,", &v, BITS_PER_LONG);

which results in hitting infinite loop at

while (a <= b) {
off = min(b - a + 1, used_size);
bitmap_set(maskp, a, off);
a += group_size;
}

due to used_size == group_size == 0.

Current code is difficult to read due to too many flag variables.
Let's rewrite it. My understanding of "range:used_size/group_size"
is "start[-end[:used_size/group_size]]" format.
Please check whether my understanding is correct...

[1] https://syzkaller.appspot.com/bug?id=ad7e0351fbc90535558514a71cd3edc11681997a

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+6887cbb011c8054e8a3d@syzkaller.appspotmail.com>
Fixes: 0a5ce0831d04382a ("lib/bitmap.c: make bitmap_parselist() thread-safe and much faster")
Cc: Yury Norov <ynorov@caviumnetworks.com>
Cc: Noam Camus <noamca@mellanox.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
lib/bitmap.c | 183 +++++++++++++++++++++++++----------------------------------
1 file changed, 78 insertions(+), 105 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 9e498c7..9cef440 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -485,6 +485,58 @@ int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
}
EXPORT_SYMBOL(bitmap_print_to_pagebuf);

+static bool get_uint(const char **buf, unsigned int *res)
+{
+ const char *p = *buf;
+
+ if (!isdigit(*p))
+ return false;
+ *res = simple_strtoul(p, (char **) buf, 10);
+ return p < *buf;
+}
+
+static int __bitmap_parse_one_chunk(const char *buf, unsigned long *maskp,
+ const unsigned int nmaskbits)
+{
+ unsigned int start;
+ unsigned int end;
+ unsigned int group_size;
+ unsigned int used_size;
+
+ while (*buf && isspace(*buf))
+ buf++;
+ if (!get_uint(&buf, &start))
+ return -EINVAL;
+ if (*buf == '-') {
+ buf++;
+ if (!get_uint(&buf, &end) || start > end)
+ return -EINVAL;
+ if (*buf == ':') {
+ buf++;
+ if (!get_uint(&buf, &used_size) || *buf++ != '/' ||
+ !get_uint(&buf, &group_size) ||
+ used_size > group_size)
+ return -EINVAL;
+ } else {
+ group_size = used_size = end - start + 1;
+ }
+ } else {
+ end = start;
+ group_size = used_size = 1;
+ }
+ if (end >= nmaskbits)
+ return -ERANGE;
+ while (start <= end) {
+ const unsigned int bits = min(end - start + 1, used_size);
+
+ bitmap_set(maskp, start, bits);
+ start += group_size;
+ }
+ while (*buf && isspace(*buf))
+ buf++;
+ return *buf ? -EINVAL : 0;
+}
+
/**
* __bitmap_parselist - convert list format ASCII string to bitmap
* @buf: read nul-terminated user string from this buffer
@@ -511,113 +563,34 @@ int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
* - ``-ERANGE``: bit number specified too large for mask
*/
static int __bitmap_parselist(const char *buf, unsigned int buflen,
- int is_user, unsigned long *maskp,
- int nmaskbits)
+ const int is_user, unsigned long *maskp,
+ const int nmaskbits)
{
- unsigned int a, b, old_a, old_b;
- unsigned int group_size, used_size, off;
- int c, old_c, totaldigits, ndigits;
- const char __user __force *ubuf = (const char __user __force *)buf;
- int at_start, in_range, in_partial_range;
-
- totaldigits = c = 0;
- old_a = old_b = 0;
- group_size = used_size = 0;
+ int err = 0;
bitmap_zero(maskp, nmaskbits);
- do {
- at_start = 1;
- in_range = 0;
- in_partial_range = 0;
- a = b = 0;
- ndigits = totaldigits;
-
- /* Get the next cpu# or a range of cpu#'s */
- while (buflen) {
- old_c = c;
- if (is_user) {
- if (__get_user(c, ubuf++))
- return -EFAULT;
- } else
- c = *buf++;
- buflen--;
- if (isspace(c))
- continue;
-
- /* A '\0' or a ',' signal the end of a cpu# or range */
- if (c == '\0' || c == ',')
- break;
- /*
- * whitespaces between digits are not allowed,
- * but it's ok if whitespaces are on head or tail.
- * when old_c is whilespace,
- * if totaldigits == ndigits, whitespace is on head.
- * if whitespace is on tail, it should not run here.
- * as c was ',' or '\0',
- * the last code line has broken the current loop.
- */
- if ((totaldigits != ndigits) && isspace(old_c))
- return -EINVAL;
-
- if (c == '/') {
- used_size = a;
- at_start = 1;
- in_range = 0;
- a = b = 0;
- continue;
- }
-
- if (c == ':') {
- old_a = a;
- old_b = b;
- at_start = 1;
- in_range = 0;
- in_partial_range = 1;
- a = b = 0;
- continue;
- }
-
- if (c == '-') {
- if (at_start || in_range)
- return -EINVAL;
- b = 0;
- in_range = 1;
- at_start = 1;
- continue;
- }
-
- if (!isdigit(c))
- return -EINVAL;
-
- b = b * 10 + (c - '0');
- if (!in_range)
- a = b;
- at_start = 0;
- totaldigits++;
- }
- if (ndigits == totaldigits)
- continue;
- if (in_partial_range) {
- group_size = a;
- a = old_a;
- b = old_b;
- old_a = old_b = 0;
- } else {
- used_size = group_size = b - a + 1;
- }
- /* if no digit is after '-', it's wrong*/
- if (at_start && in_range)
- return -EINVAL;
- if (!(a <= b) || !(used_size <= group_size))
- return -EINVAL;
- if (b >= nmaskbits)
- return -ERANGE;
- while (a <= b) {
- off = min(b - a + 1, used_size);
- bitmap_set(maskp, a, off);
- a += group_size;
- }
- } while (buflen && c == ',');
- return 0;
+ while (buflen && !err) {
+ char *cp;
+ char tmpbuf[256];
+ unsigned int size = min(buflen,
+ (unsigned int) sizeof(tmpbuf) - 1);
+
+ if (!is_user)
+ memcpy(tmpbuf, buf, size);
+ else if (copy_from_user(tmpbuf, (const char __user __force *)
+ buf, size))
+ return -EFAULT;
+ tmpbuf[size] = '\0';
+ cp = strchr(tmpbuf, ',');
+ if (cp) {
+ *cp = '\0';
+ size = cp - tmpbuf + 1;
+ } else if (size != buflen)
+ return -EINVAL; /* Chunk too long. */
+ buflen -= size;
+ buf += size;
+ err = __bitmap_parse_one_chunk(tmpbuf, maskp, nmaskbits);
+ }
+ return err;
}

int bitmap_parselist(const char *bp, unsigned long *maskp, int nmaskbits)
--
1.8.3.1

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