Messages in this thread Patch in this message | | | Date | Tue, 31 Mar 2009 15:32:23 +0200 | From | Martin Schwidefsky <> | Subject | [PATCH] do_xip_mapping_read: fix length calculation |
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From: Martin Schwidefsky <schwidefsky@de.ibm.com>
The calculation of the value nr in do_xip_mapping_read is incorrect. If the copy required more than one iteration in the do while loop the copies variable will be non-zero. The maximum length that may be passed to the call to copy_to_user(buf+copied, xip_mem+offset, nr) is len-copied but the check only compares against (nr > len).
This bug is the cause for the heap corruption Carsten has been chasing for so long:
*** glibc detected *** /bin/bash: free(): invalid next size (normal): 0x00000000800e39f0 *** ======= Backtrace: ========= /lib64/libc.so.6[0x200000b9b44] /lib64/libc.so.6(cfree+0x8e)[0x200000bdade] /bin/bash(free_buffered_stream+0x32)[0x80050e4e] /bin/bash(close_buffered_stream+0x1c)[0x80050ea4] /bin/bash(unset_bash_input+0x2a)[0x8001c366] /bin/bash(make_child+0x1d4)[0x8004115c] /bin/bash[0x8002fc3c] /bin/bash(execute_command_internal+0x656)[0x8003048e] /bin/bash(execute_command+0x5e)[0x80031e1e] /bin/bash(execute_command_internal+0x79a)[0x800305d2] /bin/bash(execute_command+0x5e)[0x80031e1e] /bin/bash(reader_loop+0x270)[0x8001efe0] /bin/bash(main+0x1328)[0x8001e960] /lib64/libc.so.6(__libc_start_main+0x100)[0x200000592a8] /bin/bash(clearerr+0x5e)[0x8001c092]
With this bug fix the commit 0e4a9b59282914fe057ab17027f55123964bc2e2 "ext2/xip: refuse to change xip flag during remount with busy inodes" can be removed again.
Cc: Carsten Otte <cotte@de.ibm.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Jared Hulbert <jaredeh@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> ---
mm/filemap_xip.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff -urpN linux-2.6/mm/filemap_xip.c linux-2.6-patched/mm/filemap_xip.c --- linux-2.6/mm/filemap_xip.c 2009-03-24 00:12:14.000000000 +0100 +++ linux-2.6-patched/mm/filemap_xip.c 2009-03-31 15:25:53.000000000 +0200 @@ -89,8 +89,8 @@ do_xip_mapping_read(struct address_space } } nr = nr - offset; - if (nr > len) - nr = len; + if (nr > len - copied) + nr = len - copied; error = mapping->a_ops->get_xip_mem(mapping, index, 0, &xip_mem, &xip_pfn);
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