Re: [PATCH] tools/xenstored: Prevent a buffer overflow in dump_state_node_perms()

[Juergen Gross <jgross@xxxxxxxx>]

On 06.05.21 18:12, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> ASAN reported one issue when Live Updating Xenstored:
>
> =================================================================
> ==873==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffc194f53e0 
> at pc 0x555c6b323292 bp 0x7ffc194f5340 sp 0x7ffc194f5338
> WRITE of size 1 at 0x7ffc194f53e0 thread T0
>      #0 0x555c6b323291 in dump_state_node_perms 
> xen/tools/xenstore/xenstored_core.c:2468
>      #1 0x555c6b32746e in dump_state_special_node 
> xen/tools/xenstore/xenstored_domain.c:1257
>      #2 0x555c6b32a702 in dump_state_special_nodes 
> xen/tools/xenstore/xenstored_domain.c:1273
>      #3 0x555c6b32ddb3 in lu_dump_state 
> xen/tools/xenstore/xenstored_control.c:521
>      #4 0x555c6b32e380 in do_lu_start xen/tools/xenstore/xenstored_control.c:660
>      #5 0x555c6b31b461 in call_delayed xen/tools/xenstore/xenstored_core.c:278
>      #6 0x555c6b32275e in main xen/tools/xenstore/xenstored_core.c:2357
>      #7 0x7f95eecf3d09 in __libc_start_main ../csu/libc-start.c:308
>      #8 0x555c6b3197e9 in _start (/usr/local/sbin/xenstored+0xc7e9)
>
> Address 0x7ffc194f53e0 is located in stack of thread T0 at offset 80 in frame
>      #0 0x555c6b32713e in dump_state_special_node 
> xen/tools/xenstore/xenstored_domain.c:1232
>
>    This frame has 2 object(s):
>      [32, 40) 'head' (line 1233)
>      [64, 80) 'sn' (line 1234) <== Memory access at offset 80 overflows this 
> variable
>
> This is happening because the callers are passing a pointer to a variable
> allocated on the stack. However, the field perms is a dynamic array, so
> Xenstored will end up to read outside of the variable.
>
> Rework the code so the permissions are written one by one in the fd.
>
> Fixes: ed6eebf17d2c ("tools/xenstore: dump the xenstore state for live update")
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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