mtdchar: fix overflows in adjustment of `count`
[ Upstream commitpull/10/head6c6bc9ea84
] 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> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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67e522a76d
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b888dba2e8
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@ -160,8 +160,12 @@ static ssize_t mtdchar_read(struct file *file, char __user *buf, size_t count,
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pr_debug("MTD_read\n");
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pr_debug("MTD_read\n");
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if (*ppos + count > mtd->size)
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if (*ppos + count > mtd->size) {
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count = mtd->size - *ppos;
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if (*ppos < mtd->size)
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count = mtd->size - *ppos;
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else
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count = 0;
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}
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if (!count)
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if (!count)
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return 0;
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return 0;
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@ -246,7 +250,7 @@ static ssize_t mtdchar_write(struct file *file, const char __user *buf, size_t c
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pr_debug("MTD_write\n");
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pr_debug("MTD_write\n");
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if (*ppos == mtd->size)
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if (*ppos >= mtd->size)
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return -ENOSPC;
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return -ENOSPC;
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if (*ppos + count > mtd->size)
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if (*ppos + count > mtd->size)
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