Messages in this thread | | | From | Arvind Sankar <> | Date | Sat, 5 Sep 2020 19:16:44 -0400 | Subject | Re: [RFC PATCH 2/2] x86/cmdline: Use strscpy to initialize boot_command_line |
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On Sat, Sep 05, 2020 at 03:59:04PM -0700, Randy Dunlap wrote: > On 9/5/20 3:23 PM, Arvind Sankar wrote: > > The x86 boot protocol requires the kernel command line to be a > > NUL-terminated string of length at most COMMAND_LINE_SIZE (including the > > terminating NUL). In case the bootloader messed up and the command line > > is too long (hence not NUL-terminated), use strscpy to copy the command > > line into boot_command_line. This ensures that boot_command_line is > > NUL-terminated, and it also avoids accessing beyond the actual end of > > the command line if it was properly NUL-terminated. > > > > Note that setup_arch() will already force command_line to be > > NUL-terminated by using strlcpy(), as well as boot_command_line if a > > builtin command line is configured. If boot_command_line was not > > initially NUL-terminated, the strlen() inside of strlcpy()/strlcat() > > will run beyond boot_command_line, but this is almost certainly > > harmless in practice. > > > > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> > > Hi, > Just for my enlightenment, what would be wrong with: > > (which is done in arch/m68/kernel/setup_no.c) > > > --- > > arch/x86/kernel/head64.c | 2 +- > > arch/x86/kernel/head_32.S | 11 +++++------ > > 2 files changed, 6 insertions(+), 7 deletions(-) > > > > diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c > > index cbb71c1b574f..740dd05b9462 100644 > > --- a/arch/x86/kernel/head64.c > > +++ b/arch/x86/kernel/head64.c > > @@ -410,7 +410,7 @@ static void __init copy_bootdata(char *real_mode_data) > > cmd_line_ptr = get_cmd_line_ptr(); > > if (cmd_line_ptr) { > > command_line = __va(cmd_line_ptr); > > memcpy(boot_command_line, command_line, COMMAND_LINE_SIZE); > > + boot_command_line[COMMAND_LINE_SIZE - 1] = 0; > > } > > > > /* > > > thanks. > -- > ~Randy >
That still accesses beyond the end of the bootloader's command line, which could theoretically be a bad thing: eg the EFI stub only allocates enough space for the actual length of the command line, rather than the full COMMAND_LINE_SIZE. But yeah, that was my first version of this patch.
> > NUL-terminated, and it also avoids accessing beyond the actual end of > > the command line if it was properly NUL-terminated.
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