block: do_mounts - accept root=<non-existant partition>

Some devices, like md, may create partitions only at first access,
so allow root= to be set to a valid non-existant partition of an
existing disk. This applies only to non-initramfs root mounting.

This fixes a regression from 2.6.24 which did allow this to happen and
broke some users machines :(

Acked-by: Neil Brown <neilb@suse.de>
Tested-by: Joao Luis Meloni Assirati <assirati@nonada.if.usp.br>
Cc: stable <stable@kernel.org>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 26 insertions, 1 deletions

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 3885e70e7759..660c1e50c91b 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -76,6 +76,7 @@ dev_t name_to_dev_t(char *name)
         char s[32];
         char *p;
         dev_t res = 0;
+        int part;
 
         if (strncmp(name, "/dev/", 5) != 0) {
                 unsigned maj, min;
@@ -106,7 +107,31 @@ dev_t name_to_dev_t(char *name)
         for (p = s; *p; p++)
                 if (*p == '/')
                         *p = '!';
-        res = blk_lookup_devt(s);
+        res = blk_lookup_devt(s, 0);
+        if (res)
+                goto done;
+
+        /*
+         * try non-existant, but valid partition, which may only exist
+         * after revalidating the disk, like partitioned md devices
+         */
+        while (p > s && isdigit(p[-1]))
+                p--;
+        if (p == s || !*p || *p == '0')
+                goto fail;
+
+        /* try disk name without <part number> */
+        part = simple_strtoul(p, NULL, 10);
+        *p = '\0';
+        res = blk_lookup_devt(s, part);
+        if (res)
+                goto done;
+
+        /* try disk name without p<part number> */
+        if (p < s + 2 || !isdigit(p[-2]) || p[-1] != 'p')
+                goto fail;
+        p[-1] = '\0';
+        res = blk_lookup_devt(s, part);
         if (res)
                 goto done;