Bug #13324

struct dk_minfo_ext size differences trigger SSP in libfdisk

Added by Jason King 9 days ago. Updated 6 days ago.

Start date:
Due date:
% Done:


Estimated time:
Gerrit CR:


Unfortunately, the 64-bit version of struct dk_minfo_ext has an extra 4 bytes of padding over the 32-bit version. This was discovered after the zfs tests were run on a system built with the stack smashing protection (SSP):

root@pi:/var/tmp/test_results/20201120T103646# mdb /usr/sbin/format core
Loading modules: [ ]
> ::sizeof struct dk_minfo_ext
sizeof (struct dk_minfo_ext) = 0x14
root@pi:/var/tmp/test_results/20201120T103646# mdb -k
Loading modules: [ unix genunix specfs dtrace mac cpu.generic uppc apix scsi_vhci zfs ip hook neti sockfs arp usba smbios stmf stmf_sbd mm lofs random cpc crypto ufs logindmux nsmb ptm smbsrv nfs ipc ]
> ::sizeof struct dk_minfo_ext
sizeof (struct dk_minfo_ext) = 0x18

From the definition of struct dk_minfo_ext, the reason is straightforward:

 * Used for Media info or the current profile info
 * including physical block size if supported.
struct dk_minfo_ext {
        uint_t          dki_media_type; /* Media type or profile info */
        uint_t          dki_lbsize;     /* Logical blocksize of media */
        diskaddr_t      dki_capacity;   /* Capacity as # of dki_lbsize blks */
        uint_t          dki_pbsize;     /* Physical blocksize of media */

For 64-bit, an extra 4 bytes of padding is appended to the end of the struct. Since there is no separate 32-bit version, all of the existing kernel drivers that implement DKIOCGMEDIAINFOEXT have been copying out an extra 4 bytes of data. This was seen in the zfs tests since the format command uses libfdisk which issues this ioctl, causing a stack similar to:

> ::stack`syscall+0x13(febac144, 1c, 251f153, 0, 8036ad8, fee64000)
0xfeb2d1ff(84f75e0)`__stack_chk_fail_local+0x17(fee50e71, fef10018, feadac78, 84f75e0, 40, 10)`fdisk_init_master_part_table(84f89e8)`fdisk_init_master_part_table+0x26(84f89e8)`libfdisk_init+0x216(80370b0, 8036c6c, 0, 1)
extpart_init+0x2f(80370b0, 84f6da8, 200, feb1b2f9, fec0080c, f18570a8)
copy_solaris_part+0x109(84f5e84, 1, 0, 8066064)
init_globals+0x351(84f5e28, 84f5e28, 0, 80663da)
main+0x3a6(803781c, fec0d628, 8037858, 8057ed7, 7, 803787c)
_start_crt+0x96(7, 803787c, f182c6f1, 0, 0, 0)
_start+0x1a(7, 8037ad0, 8037ad7, 8037ada, 8037add, 8037ae0)

Updated by Jason King 9 days ago

  • Subject changed from struct dk_minfo_ext size differences trigger SSP protection in libfdisk to struct dk_minfo_ext size differences trigger SSP in libfdisk

Updated by Jason King 9 days ago

  • Description updated (diff)

Updated by Electric Monk 6 days ago

  • Gerrit CR set to 1075

Also available in: Atom PDF