efi/libstub: Fix path separator regression

Commit 9302c1bb8e47 ("efi/libstub: Rewrite file I/O routine") introduced a
regression that made a couple of (badly configured) systems fail to
boot [1]: Until 5.6, we silently accepted Unix-style file separators in
EFI paths, which might violate the EFI standard, but are an easy to make
mistake. This fix restores the pre-5.7 behaviour.

[1] https://bbs.archlinux.org/viewtopic.php?id=256273

Fixes: 9302c1bb8e47 ("efi/libstub: Rewrite file I/O routine")
Signed-off-by: Philipp Fent <fent@in.tum.de>
Link: https://lore.kernel.org/r/20200615115109.7823-1-fent@in.tum.de
[ardb: rewrite as chained if/else statements]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/drivers/firmware/efi/libstub/file.c b/drivers/firmware/efi/libstub/file.c
index 2005e33..630caa6 100644 (file)
--- a/drivers/firmware/efi/libstub/file.c
+++ b/drivers/firmware/efi/libstub/file.c
@@ -102,12 +102,20 @@ static int find_file_option(const efi_char16_t *cmdline, int cmdline_len,
        if (!found)
                return 0;
 
+       /* Skip any leading slashes */
+       while (cmdline[i] == L'/' || cmdline[i] == L'\\')
+               i++;
+
        while (--result_len > 0 && i < cmdline_len) {
-               if (cmdline[i] == L'\0' ||
-                   cmdline[i] == L'\n' ||
-                   cmdline[i] == L' ')
+               efi_char16_t c = cmdline[i++];
+
+               if (c == L'\0' || c == L'\n' || c == L' ')
                        break;
-               *result++ = cmdline[i++];
+               else if (c == L'/')
+                       /* Replace UNIX dir separators with EFI standard ones */
+                       *result++ = L'\\';
+               else
+                       *result++ = c;
        }
        *result = L'\0';
        return i;