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rework update_dcb() to avoid potential access uninitialized memory

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This commit is contained in:
Kenneth J Davis 2024-02-03 21:09:45 -05:00
parent 1c2f541689
commit 431be02b0a
2 changed files with 28 additions and 9 deletions
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2
kernel/kernel.asm
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@ -519,7 +519,7 @@ _first_mcb dw 0 ;-0002 Start of user memory
global MARK0026H global MARK0026H
; A reference seems to indicate that this should start at offset 26h. ; A reference seems to indicate that this should start at offset 26h.
MARK0026H equ $ MARK0026H equ $
_DPBp dd 0 ; 0000 First drive Parameter Block _DPBp dd -1 ; 0000 First drive Parameter Block
global _sfthead global _sfthead
_sfthead dd 0 ; 0004 System File Table head _sfthead dd 0 ; 0004 System File Table head
global _clock global _clock

35
kernel/main.c
View File

@ -532,20 +532,35 @@ STATIC VOID update_dcb(struct dhdr FAR * dhp)
COUNT nunits = dhp->dh_name[0]; COUNT nunits = dhp->dh_name[0];
struct dpb FAR *dpb; struct dpb FAR *dpb;
/* printf("nblkdev = %i\n", LoL->nblkdev); */
/* if no units, nothing to do, ensure at least 1 unit for rest of logic */
if (nunits == 0) return;
/* allocate memory for new device control blocks, insert into chain [at end], and update our pointer to new end */
dpb = (struct dpb FAR *)KernelAlloc(nunits * sizeof(struct dpb), 'E', Config.cfgDosDataUmb);
/* find end of dpb chain or initialize root if needed */
if (LoL->nblkdev == 0) if (LoL->nblkdev == 0)
dpb = LoL->DPBp; {
/* update root pointer to new end (our just allocated block) */
LoL->DPBp = dpb;
}
else else
{ {
for (dpb = LoL->DPBp; (ULONG) dpb->dpb_next != 0xffffffffl; struct dpb FAR *tmp_dpb;
dpb = dpb->dpb_next) /* find current end of dpb chain by following next pointers to end */
for (tmp_dpb = LoL->DPBp; (ULONG) tmp_dpb->dpb_next != 0xffffffffl; tmp_dpb = dpb->dpb_next)
; ;
dpb = dpb->dpb_next = /* insert into chain [at end] */
KernelAlloc(nunits * sizeof(struct dpb), 'E', Config.cfgDosDataUmb); tmp_dpb->dpb_next = dpb;
} }
/* dpb points to last block, one just allocated */
for (Index = 0; Index < nunits; Index++) for (Index = 0; Index < nunits; Index++)
{ {
dpb->dpb_next = dpb + 1; /* printf("processing unit %i of %i nunits\n", Index, nunits); */
dpb->dpb_next = dpb + 1; /* memory allocated as array, so next is just next element */
dpb->dpb_unit = LoL->nblkdev; dpb->dpb_unit = LoL->nblkdev;
dpb->dpb_subunit = Index; dpb->dpb_subunit = Index;
dpb->dpb_device = dhp; dpb->dpb_device = dhp;
@ -555,10 +570,14 @@ STATIC VOID update_dcb(struct dhdr FAR * dhp)
LoL->CDSp[LoL->nblkdev].cdsDpb = dpb; LoL->CDSp[LoL->nblkdev].cdsDpb = dpb;
LoL->CDSp[LoL->nblkdev].cdsFlags = CDSPHYSDRV; LoL->CDSp[LoL->nblkdev].cdsFlags = CDSPHYSDRV;
} }
++dpb;
++dpb; /* dbp = dbp->dpb_next; */
++LoL->nblkdev; ++LoL->nblkdev;
} }
/* note that always at least 1 valid dpb due to above early exit if nunits==0 */
(dpb - 1)->dpb_next = (void FAR *)0xFFFFFFFFl; (dpb - 1)->dpb_next = (void FAR *)0xFFFFFFFFl;
/* printf("processed %i nunits\n", nunits); */
} }
/* If cmdLine is NULL, this is an internal driver */ /* If cmdLine is NULL, this is an internal driver */