Date: Tue, 25 Apr 2023 08:00:36 GMT From: =?utf-8?Q?Stefan=20E=C3=9Fer?= <se@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 0728695c63ef - main - fs/msdosfs: Fix potential panic and size calculations Message-ID: <202304250800.33P80a57091519@gitrepo.freebsd.org>
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The branch main has been updated by se: URL: https://cgit.FreeBSD.org/src/commit/?id=0728695c63efda298feccefb3615c23cb6682929 commit 0728695c63efda298feccefb3615c23cb6682929 Author: Stefan Eßer <se@FreeBSD.org> AuthorDate: 2023-04-25 06:35:16 +0000 Commit: Stefan Eßer <se@FreeBSD.org> CommitDate: 2023-04-25 07:58:29 +0000 fs/msdosfs: Fix potential panic and size calculations Some combinations of FAT12 file system parameters could cause a kernel panic due to an unmapped access if the size of the FAT was larger than the CPU page size. The reason is that FAT12 uses 3 bytes to store 2 FAT pointers, leading to partial FAT pointers at the end of buffers of a size that is not a multiple of 3. With a typical page size of 4 KB, this caused the FAT entry at byte offsets 4095 and 4096 to cross the page boundary, with only the first page mapped. This was fixed by adjusting the mapping to always cover both bytes of each FAT entry. Testing revealed 2 other inconsistencies that are fixed by this commit: 1) The calculation of the size of the data area did not take into account the fact that the first two data block numbers are reserved and that the data area starts with block 2. This could cause a FAT12 file system created with the maximum supported number of blocks to be incorrectly identified as FAT16. 2) The root directory does not take up space in the data area of a FAT12 or FAT16 file system, since it is placed into a reserved area outside of that data area. This commits makes stat() report the logical size of the root directory, but with 0 blocks allocated from the data area. PR: 270587 Reviewed by: mckusick Differential Revision: https://reviews.freebsd.org/D39386 --- sys/fs/msdosfs/msdosfs_fat.c | 12 +++++++++--- sys/fs/msdosfs/msdosfs_vfsops.c | 15 +++++++++------ sys/fs/msdosfs/msdosfs_vnops.c | 7 +++++-- 3 files changed, 23 insertions(+), 11 deletions(-) diff --git a/sys/fs/msdosfs/msdosfs_fat.c b/sys/fs/msdosfs/msdosfs_fat.c index e6d9b671e7d7..2d50d30f33b3 100644 --- a/sys/fs/msdosfs/msdosfs_fat.c +++ b/sys/fs/msdosfs/msdosfs_fat.c @@ -89,11 +89,17 @@ static void fatblock(struct msdosfsmount *pmp, u_long ofs, u_long *bnp, u_long *sizep, u_long *bop) { - u_long bn, size; + u_long bn, size, fatblocksec; + fatblocksec = pmp->pm_fatblocksec; + if (FAT12(pmp) && fatblocksec % 3 != 0) { + fatblocksec *= 3; + if (fatblocksec % 6 == 0) + fatblocksec /= 2; + } bn = ofs / pmp->pm_fatblocksize * pmp->pm_fatblocksec; - size = min(pmp->pm_fatblocksec, pmp->pm_FATsecs - bn) - * DEV_BSIZE; + size = roundup(min(fatblocksec, pmp->pm_FATsecs - bn) * DEV_BSIZE, + pmp->pm_BlkPerSec * DEV_BSIZE); bn += pmp->pm_fatblk + pmp->pm_curfat * pmp->pm_FATsecs; if (bnp) diff --git a/sys/fs/msdosfs/msdosfs_vfsops.c b/sys/fs/msdosfs/msdosfs_vfsops.c index e2b1fd6b91f5..87e150e0e18a 100644 --- a/sys/fs/msdosfs/msdosfs_vfsops.c +++ b/sys/fs/msdosfs/msdosfs_vfsops.c @@ -700,11 +700,14 @@ mountmsdosfs(struct vnode *odevvp, struct mount *mp) } pmp->pm_maxcluster = (pmp->pm_HugeSectors - pmp->pm_firstcluster) / SecPerClust + 1; - pmp->pm_fatsize = pmp->pm_FATsecs * DEV_BSIZE; /* XXX not used? */ + pmp->pm_fatsize = pmp->pm_FATsecs * DEV_BSIZE; if (pmp->pm_fatmask == 0) { - if (pmp->pm_maxcluster <= ((CLUST_RSRVD - CLUST_FIRST) & - FAT12_MASK)) { + /* + * The last 10 (or 16?) clusters are reserved and must not + * be allocated for data. + */ + if (pmp->pm_maxcluster < (CLUST_RSRVD & FAT12_MASK)) { /* * This will usually be a floppy disk. This size makes * sure that one FAT entry will not be split across @@ -720,11 +723,11 @@ mountmsdosfs(struct vnode *odevvp, struct mount *mp) } } - clusters = (pmp->pm_fatsize / pmp->pm_fatmult) * pmp->pm_fatdiv; + clusters = (pmp->pm_fatsize / pmp->pm_fatmult) * pmp->pm_fatdiv ; if (pmp->pm_maxcluster >= clusters) { #ifdef MSDOSFS_DEBUG printf("Warning: number of clusters (%ld) exceeds FAT " - "capacity (%ld)\n", pmp->pm_maxcluster + 1, clusters); + "capacity (%ld)\n", pmp->pm_maxcluster - 1, clusters); #endif pmp->pm_maxcluster = clusters - 1; } @@ -1045,7 +1048,7 @@ msdosfs_statfs(struct mount *mp, struct statfs *sbp) pmp = VFSTOMSDOSFS(mp); sbp->f_bsize = pmp->pm_bpcluster; sbp->f_iosize = pmp->pm_bpcluster; - sbp->f_blocks = pmp->pm_maxcluster + 1; + sbp->f_blocks = pmp->pm_maxcluster - CLUST_FIRST + 1; sbp->f_bfree = pmp->pm_freeclustercount; sbp->f_bavail = pmp->pm_freeclustercount; sbp->f_files = howmany(pmp->pm_rootdirsize * DEV_BSIZE, diff --git a/sys/fs/msdosfs/msdosfs_vnops.c b/sys/fs/msdosfs/msdosfs_vnops.c index f095a4abea62..bc47f9dde574 100644 --- a/sys/fs/msdosfs/msdosfs_vnops.c +++ b/sys/fs/msdosfs/msdosfs_vnops.c @@ -313,8 +313,11 @@ msdosfs_getattr(struct vop_getattr_args *ap) vap->va_flags |= UF_SYSTEM; vap->va_gen = 0; vap->va_blocksize = pmp->pm_bpcluster; - vap->va_bytes = - (dep->de_FileSize + pmp->pm_crbomask) & ~pmp->pm_crbomask; + if (dep->de_StartCluster != MSDOSFSROOT) + vap->va_bytes = + (dep->de_FileSize + pmp->pm_crbomask) & ~pmp->pm_crbomask; + else + vap->va_bytes = 0; /* FAT12/FAT16 root dir in reserved area */ vap->va_type = ap->a_vp->v_type; vap->va_filerev = dep->de_modrev; return (0);
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