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The binary representation of the superblock (the fs structure) is written

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out verbatim to the disk: see ffs_sbput() in sys/ufs/ffs/ffs_subr.c.
It contains a pointer to the fs_summary_info structure. This pointer
value inadvertently causes garbage to be stored. It is garbage because
the pointer to the fs_summary_info structure is the address the then
current stack or heap. Although a mere pointer does not reveal anything
useful (like a part of a private key) to an attacker, garbage output
deteriorates reproducibility.

This commit zeros out the pointer to the fs_summary_info structure
before writing the out the superblock.

Reviewed by:  kib
Tested by:    Peter Holm
PR:           246983
Sponsored by: Netflix
This commit is contained in:
Kirk McKusick 2020-06-19 01:04:25 +00:00
parent 34816cb9ae
commit 93440bbefd
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=362359
2 changed files with 18 additions and 6 deletions
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23
sys/ufs/ffs/ffs_subr.c
View File

@ -50,7 +50,6 @@ uint32_t ffs_calc_sbhash(struct fs *);
struct malloc_type;
#define UFS_MALLOC(size, type, flags) malloc(size)
#define UFS_FREE(ptr, type) free(ptr)
#define UFS_TIME time(NULL)
/*
* Request standard superblock location in ffs_sbget
*/
@ -78,7 +77,6 @@ struct malloc_type;
#define UFS_MALLOC(size, type, flags) malloc(size, type, flags)
#define UFS_FREE(ptr, type) free(ptr, type)
#define UFS_TIME time_second
#endif /* _KERNEL */
@ -349,11 +347,24 @@ ffs_sbput(void *devfd, struct fs *fs, off_t loc,
}
}
fs->fs_fmod = 0;
fs->fs_time = UFS_TIME;
#ifndef _KERNEL
{
struct fs_summary_info *fs_si;
fs->fs_time = time(NULL);
/* Clear the pointers for the duration of writing. */
fs_si = fs->fs_si;
fs->fs_si = NULL;
fs->fs_ckhash = ffs_calc_sbhash(fs);
error = (*writefunc)(devfd, loc, fs, fs->fs_sbsize);
fs->fs_si = fs_si;
}
#else /* _KERNEL */
fs->fs_time = time_second;
fs->fs_ckhash = ffs_calc_sbhash(fs);
if ((error = (*writefunc)(devfd, loc, fs, fs->fs_sbsize)) != 0)
return (error);
return (0);
error = (*writefunc)(devfd, loc, fs, fs->fs_sbsize);
#endif /* _KERNEL */
return (error);
}
/*

1
sys/ufs/ffs/ffs_vfsops.c
View File

@ -2293,6 +2293,7 @@ ffs_use_bwrite(void *devfd, off_t loc, void *buf, int size)
bcopy((caddr_t)fs, bp->b_data, (u_int)fs->fs_sbsize);
fs = (struct fs *)bp->b_data;
ffs_oldfscompat_write(fs, ump);
fs->fs_si = NULL;
/* Recalculate the superblock hash */
fs->fs_ckhash = ffs_calc_sbhash(fs);
if (devfdp->suspended)