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mtdchar: fix overflows in adjustment of count

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The first checks in mtdchar_read() and mtdchar_write() attempt to limit
`count` such that `*ppos + count <= mtd->size`. However, they ignore the
possibility of `*ppos > mtd->size`, allowing the calculation of `count` to
wrap around. `mtdchar_lseek()` prevents seeking beyond mtd->size, but the
pread/pwrite syscalls bypass this.

I haven't found any codepath on which this actually causes dangerous
behavior, but it seems like a sensible change anyway.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
This commit is contained in:
Jann Horn 2018-07-07 05:37:22 +02:00 committed by Boris Brezillon
parent 89fd23efa0
commit 6c6bc9ea84
1 changed files with 7 additions and 3 deletions
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10
drivers/mtd/mtdchar.c
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@ -160,8 +160,12 @@ static ssize_t mtdchar_read(struct file *file, char __user *buf, size_t count,
pr_debug("MTD_read\n");
if (*ppos + count > mtd->size)
count = mtd->size - *ppos;
if (*ppos + count > mtd->size) {
if (*ppos < mtd->size)
count = mtd->size - *ppos;
else
count = 0;
}
if (!count)
return 0;
@ -246,7 +250,7 @@ static ssize_t mtdchar_write(struct file *file, const char __user *buf, size_t c
pr_debug("MTD_write\n");
if (*ppos == mtd->size)
if (*ppos >= mtd->size)
return -ENOSPC;
if (*ppos + count > mtd->size)