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contentenc: reserve one additional block in CReqPool 

...to account for unaligned reads.

I have not seen this happen in the wild because the kernel
always seems to issue 4k-aligned requests. But the cost
of the additional block in the pool is low and prevents
a buffer overrun panic when an unaligned read does happen.
This commit is contained in:
Jakob Unterwurzacher 2017-10-19 09:23:10 +02:00
parent 2783eadc8f
commit 29445c976d
1 changed files with 13 additions and 5 deletions
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18
internal/contentenc/content.go
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@ -53,13 +53,18 @@ type ContentEnc struct {
allZeroNonce []byte
// Force decode even if integrity check fails (openSSL only)
forceDecode bool
// Ciphertext block pool. Always returns cipherBS-sized byte slices.
// Ciphertext block "sync.Pool" pool. Always returns cipherBS-sized byte
// slices (usually 4128 bytes).
cBlockPool bPool
// Ciphertext request data pool. Always returns byte slices of size
// fuse.MAX_KERNEL_WRITE + overhead.
CReqPool bPool
// Plaintext block pool. Always returns plainBS-sized byte slices.
// Plaintext block pool. Always returns plainBS-sized byte slices
// (usually 4096 bytes).
pBlockPool bPool
// Ciphertext request data pool. Always returns byte slices of size
// fuse.MAX_KERNEL_WRITE + encryption overhead.
// Used by Read() to temporarily store the ciphertext as it is read from
// disk.
CReqPool bPool
// Plaintext request data pool. Slice have size fuse.MAX_KERNEL_WRITE.
PReqPool bPool
}
@ -69,6 +74,9 @@ func New(cc *cryptocore.CryptoCore, plainBS uint64, forceDecode bool) *ContentEn
cipherBS := plainBS + uint64(cc.IVLen) + cryptocore.AuthTagLen
// Take IV and GHASH overhead into account.
cReqSize := int(fuse.MAX_KERNEL_WRITE / plainBS * cipherBS)
// An unaligned read (could happen with O_DIRECT?) may touch one
// additional ciphertext block. Reserve space for it.
cReqSize += int(cipherBS)
if fuse.MAX_KERNEL_WRITE%plainBS != 0 {
log.Panicf("unaligned MAX_KERNEL_WRITE=%d", fuse.MAX_KERNEL_WRITE)
}