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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Mon, 18 Jan 2021 11:46:39 +1100
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Subject: [PATCH] fs/fshelp: Catch impermissibly large block sizes in read
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helper
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A fuzzed HFS+ filesystem had log2blocksize = 22. This gave
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log2blocksize + GRUB_DISK_SECTOR_BITS = 31. 1 << 31 = 0x80000000,
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which is -1 as an int. This caused some wacky behavior later on in
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the function, leading to out-of-bounds writes on the destination buffer.
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Catch log2blocksize + GRUB_DISK_SECTOR_BITS >= 31. We could be stricter,
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but this is the minimum that will prevent integer size weirdness.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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---
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grub-core/fs/fshelp.c | 19 +++++++++++++++++++
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1 file changed, 19 insertions(+)
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diff --git a/grub-core/fs/fshelp.c b/grub-core/fs/fshelp.c
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index 42bd542bbc3..7e7387e86e1 100644
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--- a/grub-core/fs/fshelp.c
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+++ b/grub-core/fs/fshelp.c
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@@ -252,6 +252,25 @@ grub_fshelp_read_file (grub_disk_t disk, grub_fshelp_node_t node,
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grub_disk_addr_t i, blockcnt;
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int blocksize = 1 << (log2blocksize + GRUB_DISK_SECTOR_BITS);
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+ /*
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+ * Catch blatantly invalid log2blocksize. We could be a lot stricter, but
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+ * this is the most permissive we can be before we start to see integer
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+ * overflow/underflow issues.
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+ */
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+ if (log2blocksize + GRUB_DISK_SECTOR_BITS >= 31)
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+ {
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+ grub_error (GRUB_ERR_OUT_OF_RANGE,
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+ N_("blocksize too large"));
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+ return -1;
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+ }
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+
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+ if (pos > filesize)
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+ {
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+ grub_error (GRUB_ERR_OUT_OF_RANGE,
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+ N_("attempt to read past the end of file"));
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+ return -1;
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+ }
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+
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/* Adjust LEN so it we can't read past the end of the file. */
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if (pos + len > filesize)
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len = filesize - pos;
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