Messages in this thread | | | Subject | Re: [PATCH v2 RESEND] m68k/kernel: array out of bound access in process_uboot_commandline | From | Greg Ungerer <> | Date | Mon, 17 Jan 2022 14:03:45 +1000 |
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Hi Hangyu,
On 13/1/22 11:58 am, Hangyu Hua wrote: > When the size of commandp >= size, array out of bound write occurs because > len == 0. > > Signed-off-by: Hangyu Hua <hbh25y@gmail.com> > --- > arch/m68k/kernel/uboot.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/m68k/kernel/uboot.c b/arch/m68k/kernel/uboot.c > index 928dbd33fc4a..63eaf3c3ddcd 100644 > --- a/arch/m68k/kernel/uboot.c > +++ b/arch/m68k/kernel/uboot.c > @@ -101,5 +101,6 @@ __init void process_uboot_commandline(char *commandp, int size) > } > > parse_uboot_commandline(commandp, len); > - commandp[len - 1] = 0; > + if (len > 0) > + commandp[len - 1] = 0; > } >
I am not convinced this is wrong for the reason you think it is. Looking at the code in its entirety:
__init void process_uboot_commandline(char *commandp, int size) { int len, n;
n = strnlen(commandp, size); commandp += n; len = size - n; if (len) { /* Add the whitespace separator */ *commandp++ = ' '; len--; }
parse_uboot_commandline(commandp, len); commandp[len - 1] = 0; }
"commandp" is moved based on the return of the strnlen(). So in the case of commandp actually being full of valid characters (so n == size, and thus len == 0) the commandp technically points outside of its real size at that point. But "command[[len - 1]" would actually be pointing to the last char in the original commandp array (so the original commandp[size - 1]). Well at least if you are happy with the use of negative array indexes.
Clearly this could be structured better. There is no point in calling parse_uboot_commandline() if len == 0, or even if len == 1, since you cannot add anymore to the command line, it is full.
Regards Greg
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